The home of Australian Boulder Opal

Queensland produces boulder opal, an unique type of opal which is found attached to a host rock, ironstone. Boulder opal is unique to Queensland, and occurs in deposits in weathered sedimentary Cretaceous rocks in the west of the state.

Much opal mining in Queensland is carried out in ‘open cut’ mining operations, which is vastly different to shaft mining.

The Queensland opal fields are within a belt of deeply weathered Cretaceous sedimentary rocks known as the Winton Formation, which extends in a north-westerly direction from the New South Wales border at Hungerford stretching west of Cunnamulla, Quilpie, Longreach and Winton to Kynuna, a distance of about 1000 km.

Queensland’s opal mining fields are located in the west and southwest of the State, and include:

Yowah field (the southernmost field centred on the small town of Yowah—includes Black Gate)

Koroit field (north-east of Yowah)

Toompine field (east and south-east of Toompine—includes Lushingtons, Coparella, Duck Creek, Sheep Station Creek and Emu Creek)

Quilpie field (west and north north-west of Quilpie—includes some of the more productive mines in recent times—Pinkilla, Bull Creek, Harlequin, and probably the most famous of all, the Hayricks.

Kyabra-Eromanga field (west and north-west of Eromanga)

Bulgroo field (north of Quilpie field in the Cheviot Range—includes the Bulgroo, or Germans—and Budgerigar to the north )

Yaraka field—includes the mines in the Macedon Range, such as Mount Tighe

Jundah field (west of Jundah over the Thompson River—includes Jundah and Opalville mines)

Opalton-Mayneside field (centred on the old abandoned township of Opalton, and to the south in the Horse Creek – Mount Vergemont area)

Kynuna field—the most northerly field, south of the township of Kynuna.

Boulder opal is widely distributed in rocks in these areas, in generally elongated or ellipsoidal siliceous ironstone concretions or boulders ranging in size from less than a few centimetres to more than 20 cm. Concretions up to 5 cm across, known as ‘nuts’, may host a kernel of solid opal or contain a network of thin veins of opal through the ironstone. This variety of opal is prevalent at Yowah where the concretions form distinct bands—the well known ‘Yowah-nuts’.

These opal fields lie within a 300 km-wide belt of deeply weathered Cretaceous sedimentary rocks known as the Winton Formation. This extends north-north-west from Hungerford on the New South Wales border, west of the townships of Cunnamulla, Quilpie, Longreach and Winton, to Kynuna, a distance of about 1000 km.

Boulder opal is widely distributed in rocks in these areas, in generally elongated or ellipsoidal ironstone concretions or boulders, from a few centimetres, to up to 3 m across. The boulders may be confined to one or more layers or randomly distributed through the weathered sandstone. Their composition ranges from sandstone types (a rim or crust of ferruginised sandstone surrounding a sandstone core) or ironstone types (composed almost entirely of iron oxides).

The opal occurs as a filling or lining between the concentric layers or in radial or random cracks in the ironstone, or as a kernel in smaller concretions or nuts. (as found at Yowah and Koroit fields, the famous ‘Yowah-nuts’). Matrix opal is where the opal occurs as a network of veins or infilling of voids or between grains of the host rock (ferruginous sandstone or ironstone). Rare seam or band opal is also found and is typically encased in ironstone.

Pipe opal occurs in pipe-like structures which may be up to several centimetres in diameter within the sandstone and these structures may be hollow or opal-filled. Wood opal is occasionally found replacing woody tissue material.

As opposed to other sedimentary precious opal, boulder opal is attached to the ironstone, and stones are usually cut with the natural ironstone backing intact. Solid opals may be cut from the ironstone material where the opal is of sufficient thickness. Boulder opals are fashioned to standard shapes and sizes but are also cut in freeform shapes to highlight their individual beauty and to avoid wastage. Magnificent picture stones are also cut but these are mainly of interest to collectors rather than for jewellery use.

Quilpie opal fields

Looking for colour? In these parts there’s plenty of it, to be found both in the stories relating to the early settlement of the region and also that ‘colour’ which is sought from beneath the surface of the bush earth. Quilpie is best known as an opal town. It is often referred to as the home of the ‘Boulder Opal’ as the area is the largest producer of this type of opal in the world.

Located 980 kilometres west of Brisbane and 208 kilometres west of Charleville, Quilpie is the commercial and social centre of the Quilpie Shire. The name of the town was derived from the Aboriginal word ‘Quilpeta’ meaning Stone Curlew.

Relatively young, Quilpie was declared an official town on 29 April 1917, in the same year the railway line from Charleville to Quilpie was completed. Quilpie is rich in grazing history beginning with the pioneering efforts of families such as the Costello’s, Tully’s and Duracks.

Quilpie is located on the banks of the Bullo River in the famous Channel Country of western Queensland. The shire is supported through primary industries such as sheep, cattle grazing, oil, gas and opal mining. Apart from these main industries Quilpie Shire houses a keen and talented artistic community.

Winton opal fields

Rich in history, Winton was originally known as Pelican Waterhole and was first settled in 1875. The town is best known as the place that Banjo Paterson wrote Waltzing Matilda in 1895, whilst at Dagworth Station outside Winton. The first performance of the ballad was reported to be at Winton’s North Gregory Hotel on the 6th of April of the same year. Winton is recognised as the ‘home’ of Australian bush poetry, hosting the annual Bronze Swagman Award, one of the country’s most prestigious literary awards.

Queensland and Northern Territory Aerial Service (Qantas), Australia’s national airline was formed in Winton in November, 1920 and its first board meeting was held in the Winton Club on 21st February 1921.

During the Great Shearers’ Strike in the 1890s, 500 shearers camped just south of Winton and the town was placed under marshal law. This was the beginning of the foundation of the Labor Party.

Winton is famous for its water supply which thrusts its way to the earth’s surface from three artesian bores, all around 1,200 metres deep emerging at a temperature of 83 degrees celsius. The water is sourced from the Great Artesian Basin which provides water for most of Australia’s outback.

Winton is in the centre of Matilda Country, a diverse region in which vast mitchell grass plains are broken by magnificent coloured gorges, ridges and jump-ups. Visitors to the region will be amazed by the vastness of the plains and the undulating nature of the landscape. There is a wide variety of animal and bird life in the area, generally best seen around dusk and dawn on minor roads and tracks.

Day trips from Winton take visitors to Opalton, one of the oldest opal fields in Queensland; Combo Waterhole, where the swaggie of ‘Waltzing Matilda’ fame reputedly met his fate; the vintage sandstone homestead of Old Cork Station; and Lark Quarry, where 93 million year-old fossils capture a dinosaur stampede.

Opalton opal fields

The Opalton Field, also called the Fermoy Field was one of the largest and most extensively worked opal deposits in Queensland. It is a good example of typical opal country in western Queensland and offers the visitor the opportunity to experience first hand the remoteness and harsh conditions endured by the opal miners. Mining activity on the field is mostly limited to small-scale hand mining but some larger operations using heavy machinery are present in the surrounding area.

The Opalton Designated Fossicking Land was established in 1995 under the Fossicking Act 1994 by the then Department of Mines and Energy, with the co-operation of the Winton Shire Council and the landholder to provide for tourist and recreational fossicking. The Opalton Field is located about 124 km by road south-southwest of Winton. Travelling from Winton take the Jundah Road (mostly unsealed) and travel 15 km, turn left and travel a further 109 km (unsealed road) past Weona Homestead to Opalton. Visitors are requested not to call at ‘Weona’.

The Opalton area attracts large numbers of visitors and is popular with tourists as a place to “speck” or”noodle” fragments of opal or ironstone matrix from the surface or from the spoil dumps of old workings. However, known areas of shallow ground, such as the old Brilliant Claim area, may offer the more serious fossicker a chance to dig and find that outstanding gem.

Yowah opal fields

The Yowah opal field which includes the nearby area known as Black Gate is the southern-most opal mining centre of western Queensland. It is popular with tourists and fossickers as it has easy access from main roads and has shops, fuel, telephone, caravan park, and a permanent bore water supply. A small local population increases significantly during the winter season. The Yowah Fossicking Area has been established by the Department of Mines and Energy with the co-operation of the Council of the Shire of Paroo and the landholder to provide for tourist and recreational fossicking.

Yowah is about 160km west of Cunnamulla. Travelling towards Thargomindah, turn off to the right about 18km west of Eulo onto the Yowah / Toompine road and travel 48km via Alroy homestead to the Yowah-Quilpie turnoff. Continue a further 23km to Yowah; this last 23 km is unsealed. From Quilpie, drive 110km through Toompine to the Eulo / Yowah turnoff. Turn left and follow this mainly unsealed road for about 56km to the Yowah turnoff, and then continue the further 23km as above.

A feature of the Yowah field is the occurrence of precious opal in siliceous ironstone nodules generally referred to as “Yowah Nuts”. These nuts range from about 5mm to 200mm across, have a spherical or ellipsoidal shape, and show alternate concentric rings or bands of light and dark brown siliceous ironstone. There is sometimes a kernel of precious opal which is the main source of the gem. The nuts are found in layers (150 to 600mm in thickness) at depths up to 20m in a ferruginous sandstone, and are commonly associated with mudstone fragments or clay pellets. The main layer is located near the contact between the sandstone and underlying mudstone / claystone, but scattered nodules, and in some cases a second band, may occur above. The lateral continuity of the nut bands is somewhat difficult to predict owing to the irregular bedding of the strata, as well as the lack of any detailed
mapping. In some shafts, the nut band was not encountered, but the sandstone at its contact with the mudstone was found to be more ferruginous and cemented by partial opalisation into a hard band, which also contained opal in the form of seams and pipes.

The eastern part of the Fossicking Area has always been popular with tourists as a place to “speck” or “noodle” fragments of opal or ironstone matrix from the surface or shallow depth. In this area the main nut band appears to have been exposed at the surface, so that a layer of loose rubble of broken ironstone nut fragments covers the surface to a depth of about 600mm. Spotting chips of opal or fragments of matrix while digging through this
material is relatively easy with a bit of practice. Fragments may also occur on the spoil heaps of shafts from the old mining activities.

Opals from Queensland

Here’s a sample of the latest opals from Queensland currently available in our Australian opal catalogue:

Sources :

Queensland Holidays

“Opal in South Australia”, Mines & Energy Resources, SA

“Opal”, Qld Dept. of Mines & Energy

The home of Australian Black Opal

FAQ Where are the opal fields in Australia? Where are black opals mined? Where are the Lightning Ridge opal fields?

New South Wales produces the largest proportion of Australian opal in terms of value. Lightning Ridge is famous for producing black opal, the darkest and most valuable form of opal. White Cliffs is known for seam opal which is usually white (milk) opal or crystal opal.

Lightning Ridge opal fields

The Lightning Ridge opal mining fields are synonymous with world famous gem quality black opals. Unlike ordinary opals the black opal has carbon and iron oxide trace elements in it, producing the most sought-after opal in the world.

Legend has it that the name “Lightning Ridge” was coined after a shepherd, his dog, and six hundred sheep were killed during a fierce electrical storm, while sheltering in a low ridge in the area.

Situated in Northern New South Wales 768km from Sydney, the Ridge is home to an estimated permanent population of about 3000 who live in the town and work either servicing the miners or digging for the stones – particularly the rare black opals which are the true treasures of the district.

Population estimates for the town have proved difficult due to the transient nature of many of its inhabitants. In 2001 it had 1,826 persons, including 344 indigenous persons (18.8%) and 1,304 persons born in Australia (71.4%). The population is said to be highly variable as transient miners come and go over time.

There is an official population indicator sign on the highway as you enter the town that says, Lightning Ridge — population?. Prior to the 2004 Public Enquiry into the functioning of Walgett Shire Council, it worked on the basis that there were about 7,000 people in the town, but the enquiry found that this estimate was given no support by the 2001 census and contrasted with the 1,109 people who voted in the town at the local government elections in 2004.

Geology

Lightning Ridge lies in a large geological feature called the Surat Basin, which is part of the vast Great Australian Basin. The Great Australian Basin covers 1.7 million square kilometres of eastern Australia. It was formed when the sediments of the Basin lay at the bottom of a large inland sea. It is these sediments that later hosted the formation of precious opal.

The sedimentary host rocks are essentially horizontal. This is because they were deposited on the floor of the inland sea and have not been deformed. The rocks which host the opal at Lightning Ridge were deposited in shallow water near the edge of the Basin, probably in an estuary.

Overlying the Cretaceous sedimentary rocks are sandstones and conglomerates that were deposited by streams and rivers in the Tertiary period, about 15 million years ago. Many of these younger rocks have hardened to form silcrete and are often quarried for road materials.

Most opal at the Ridge is found between 6 and 18 metres from the surface – not so deep that they are out of the reach of smaller miners, but deep enough to make their mining hard work.

History

There is an Aboriginal explanation for the opals discovered in the Lightning Ridge area. According to legend, a huge wheel of fire fell to earth and sprayed the countryside with brilliant coloured stones.

Opal was first discovered at Lightning Ridge in the late 1880s, with the first shaft being put down around 1901 or 1902 by Jack Murray, a boundary rider who lived on a property nearby.

Some time later, a miner from Bathurst named Charlie Nettleton arrived and began sinking shafts. Nettleton had been an opal miner at White Cliffs but his luck and money ran out and he moved to Queensland. Convinced that there were more opals across the border he returned to New South Wales and started seriously prospecting on a hill, later known as Nettleton’s Hill, on Angledool Station. This was to become the site of Lightning Ridge.

The Lands Department later gazetted it as Warrangulla and it was known as that until World War 1 when it reverted to its original name. It was he who in 1903 sold the first parcel of gems from the field, receiving only $30, not even a fiftieth of the price that could have been obtained only five years later.

A number of famous stones have been found at Lightning Ridge, including the 822g ‘Big Ben’ and the ‘Flame Queen’ which was sold for £80 because the miner hadn’t eaten a proper meal for three weeks.

Tourism

Since opal was first discovered, Lightning Ridge has become synonymous with opal mining in Australia, and hence a very interesting place to visit. (Particularly during the annual goat races). Lighting Ridge offers a true vision of gritty life in the Australian outback, and the town’s mineral water spa baths (artesian bore) are great for relaxation.

The Ridge sees over 90,000 visitors per year, either fossicking for fun, looking for their fortune, or to see what an outback mining town is really like. This influx of tourists means that this once rough and ready town now boasts a number of good quality motels, an endless array of souvenir and gift shops, some good restaurants, and a veneer of civilisation.

Lightning Ridge still has a diverse range of native wildlife including kangaroos, wallabies, koalas, echidnas, possums and a remarkable range of reptiles. The town is also a haven for rare Australian birds and you can get up close and personal with a number of fascinating animals.

The township and the lure of the black opal have been neatly summed up in Laurie Hudson’s poem:

There’s a sleepy little township, out beyond the western plains,
Lightning Ridge, the town of opal, where there’s heat and scanty rains.

The location is not scenic, just rough ridges all around
Nature sired her scenes of beauty, in black opal, underground.

If you’ve never seen black opal, you have missed a splendid sight,
Like quicksilver gaily coloured, slipped through the shades of night.

Though you’ve roamed the whole world over, seen most all there is to see,
There are scenes you’ve never dreamed of, in the stone of mystery.

Lightning Ridge boasts a number of social and sporting facilities, including a golf course, pistol club and archery club. The town’s Opal Festival is held in the September-October NSW school holidays. Other annual events are the Great Goat Race at Easter and the Opal and Gem Expo in July.

White Cliffs opal fields

White Cliffs, situated in north western New South Wales, was Australia’s first viable commercial opal mining field. For about thirty-five years this field was the only major producer of opal for the world’s markets – the last year of the 19th century (1899) saw the White Cliffs opal field become the largest producer of precious opal anywhere in the world.

White Cliffs, like Coober Pedy, produces predominantly ‘seam opal’ (i.e. opal that forms in horizontal seams in the ground as opposed to small nuggets, or ‘nobbies’.) White Cliffs is also notable for producing ‘opal pineapples’ (pictured left), a strangely shaped opal fossil in the shape of a mineral crystal. These rare fossils are formed when a mineral crystal of glauberite (or ikalite) is first replaced by calcite and then opalised.

Opal was first produced in 1890, following the discovery of stones in the area by a party of kangaroo hunters in 1889. White Cliffs opal was unique in that it represented the world’s first seam opal. Consequently, this opal was easier to value, clean, manufacture, and therefore was much sought-after. The White Cliffs opal field also was uniquely rich in opalised fossils – pseudomorphs of shells, bones, and even crystals (opal pineapples). All too frequently, at the turn of the 20th Century, White Cliffs opal was sold as Hungarian opal (an opal that had not been mined in quantity for almost a century!)

In 1899 some two thousand people lived within two miles of the town area of White Cliffs. These pioneers lived in five hundred timber and iron houses, as well as countless ‘calico mansions’ fabricated from Hessian and bark, or canvas. There was an underground restaurant, bakery, and bar; but dugouts were scarce and miners mostly lived in mine shafts.

White Cliffs supplied world overseas markets for some twenty-five years; in the process restoring the ‘forgotten gem’, opal, into favour after centuries of adverse superstition. Over a century White Cliffs became an outdoor classroom for geologists; palaeontologists, government officials, and hopeful fortune-hunters. Intense summer heat drove the first miners underground – by 1900, most residents had followed suit. In 1999, ninety per cent of local residents lived in some 135 dugouts.

Opals from NSW

Here’s a sample of the latest opals from New South Wales currently available in our Australian opal catalogue:

Sources :

The Australian Gemmologist, Vol 19, #7, 1996. “The True Story of White Cliffs.”, Glen Rowe.

The Australian Gemmologist, Vol 20, #6, 1999. “White Cliffs: A Century of History.”, Glen Rowe.

Visit Outback NSW

Visit NSW

Minerals NSW

“Opal”, Qld Dept. of Mines & Energy

FAQ Where are the opal fields in Australia? Where are opals mined? Where is opal mined? Where is opal mining done? When was opal discovered?

Although there are lots of opal mining towns in Australia there are four which have become household names – Coober Pedy, Andamooka, White Cliffs and Lightning Ridge. They are wild and unruly places surrounded by a moonscape of mullock humps where people fight against horrendous climate conditions in their search for precious gemstones. They are, as one observer noted, ‘monuments to the tenacious optimism of all mankind’.

(Opal mines are indicated by an orange dot)

Currently, Australia produces around 95% of the world’s opal for use in the jewellery industry. Other countries in which opal is found in small amounts include Honduras, Mexico, former Czechoslovakia, and Brazil, however these types of opal often differ in appearance. Australian opal is considered the finest in the world.

The Australian export market for opals in 1998-99 was estimated at $60 million compared with $69 million in 1997-98 and $85 million in 1996-97. Between 2000 and 2005, production figures for uncut gems varied between $100 million and $200 million.

Australia’s Opal fields lie in the three states of Queensland, New South Wales, and South Australia, along the site of the ancient ‘Great Inland Sea’, or ‘Great Artesian Basin’. White, or ‘Milky’ opal, is found in South Australia, Black opal is found in Lightning Ridge, NSW, and Boulder opal is found in Queensland. The best time to visit the opal fields is April to September. Summer should be avoided due to the high temperatures and possible heavy rains making road access impossible in some areas.

New South Wales (NSW) – The Home of Black Opal

New South Wales produces the largest proportion of Australian opal in terms of value. Lightning Ridge is famous for producing black opal, the darkest and most valuable form of opal. Read more >

Lightning Ridge, New South Wales

The Lightning Ridge opal mining fields are synonymous with world famous gem quality black opals. Unlike ordinary opals the black opal has carbon and iron oxide trace elements in it, producing the most sought-after opal in the world.

• Read more about the Lightning Ridge opal mining fields

White Cliffs, New South Wales

White Cliffs, situated in north western New South Wales, produces predominantly white or crystal opal in the form of ‘seam opal’ (i.e. opal that forms in horizontal seams in the ground as opposed to small nuggets, or ‘nobbies’.) White Cliffs is also notable for producing ‘opal pineapples’, a strangely shaped opal fossil in the shape of a mineral crystal. These rare fossils are formed when a mineral crystal of glauberite (or ikalite) is first replaced by calcite and then opalised.

• Read more about the White Cliffs opal mining fields

Queensland (QLD) – Boulder Opal Country

Queensland produces boulder opal, an unique type of opal which is found attached to a host rock, ironstone. Boulder opal is unique to Queensland, and occurs in deposits in weathered sedimentary Cretaceous rocks in the west of the state. Read more >

Quilpie, Queensland

Looking for colour? In these parts there’s plenty of it, to be found both in the stories relating to the early settlement of the region and also that ‘colour’ which is sought from beneath the surface of the bush earth. Quilpie is best known as an opal town. It is often referred to as the home of the ‘Boulder Opal’ as the area is the largest producer of this type of opal in the world.

• Read more about the Quilpie opal mining fields

Winton, Queensland

Winton is in the centre of Matilda Country, a diverse region in which vast mitchell grass plains are broken by magnificent coloured gorges, ridges and jump-ups. Visitors to the region will be amazed by the vastness of the plains and the undulating nature of the landscape. There is a wide variety of animal and bird life in the area, generally best seen around dusk and dawn on minor roads and tracks.

• Read more about the Winton opal mining fields

Opalton, Queensland

The Opalton Field, also called the Fermoy Field was one of the largest and most extensively worked opal deposits in Queensland. It is a good example of typical opal country in western Queensland and offers the visitor the opportunity to experience first hand the remoteness and harsh conditions endured by the opal miners.

• Read more about the Opalton opal mining fields

Yowah, Queensland

The Yowah opal field is the southern-most opal mining centre of western Queensland. A feature of the Yowah field is the occurrence of precious opal in siliceous ironstone nodules generally referred to as “Yowah Nuts”.

• Read more about the Yowah opal mining fields

South Australia – The White Opal Fields

South Australia has four active opal mining fields, Andamooka, Coober Pedy, Lambina and Mintabie. South Australia is largest producer of opal in terms of volume, and produces the white opal or ‘milky’ type of opal. Read more >

Coober Pedy, South Australia

Coober Pedy produces the bulk of the world’s white opal. The opal mining fields of Coober Pedy lie in the outback of South Australia, Stuart Range, 750 km north of Adelaide. Many of the locals in Coober Pedy prefer to live underground in dugouts where it is cool in summer and warm in winter.

• Read more about the Coober Pedy opal mining fields

Andamooka, South Australia

Situated 520 km north of Adelaide, Andamooka miners work over an area of about 52 square kilometres on the Arcoona plateau in shafts, large bore-holes, open-cut excavations and small tunnels.

• Read more about the Andamooka opal mining fields

Mintabie, South Australia

A well sinker, named Larry O’Toole, is credited with finding the first opal in Mintabie in the 1920’s. Mintabie is the newest opal field, discovered in the 1920’s, but was not aggressively worked until 1978, when good opal began to be found. Mintabie is situated 180km south of the Northern Territory border, and approx. 300km north of Coober Pedy.

• Read more about the Mintabie opal mining fields

Lambina, South Australia

Old miners claim that opal was first discovered at Lambina during the depression years of the early 1930’s. A minor rush in the late 1980’s occurred following discoveries by some miners at Seven Waterholes diggings.

• Read more about the Lambina opal mining fields

The Geology of Opal

FAQ :  How is opal formed? / How are opals formed? What is the Great Artesian Basin? What is potch? What causes the formation of opal?

A Simple Explanation

Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids , caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed.

Visualise the inside of an opal, like a bag of marbles. The marbles are the silica spheres.

Smaller spheres are more commonly forming, and tend to defract the purple/ blue/ green colours.

Larger spheres are rarer forming, and tend to show off the yellow/ orange/ pink and red colours. Hence why these are the rarer colours to find in Australian Opal.

A Detailed Explanation

Occasionally, when conditions are ideal, spheres of silica, contained in silica-rich solutions in the earth form and settle under gravity in a void to form layers of silica spheres. The solution is believed to have a rate of deposition of approximately one centimetre thickness in five million years at a depth of forty metres. If the process allows spheres to reach uniform size, then precious opal commences to form. For precious opal the sphere size ranges from approximately 150 to 400 nanometres producing a play of colour by diffraction in the visible light range of 400 to 700 nanometres.

Each local opal field or occurrence must have contained voids or porosity of some sort to provide a site for opal deposition. In volcanic rocks and adjacent environments the opal appears to fill only vughs and cracks whereas in sedimentary rocks there are a variety of voids created by the weathering process. Leaching of carbonate from boulders, nodules, many different fossils, along with the existing cracks, open centres of ironstone nodules and horizontal seams provide a myriad of moulds ready for the deposition of secondary minerals such as opal.

Much of the opal deposition is not precious. It is called “potch” by the miners, or common opal by the mineralogist, as it does not show a play of colour. Opaline silica not only fills the larger voids mentioned but also may fill the pore space in silt and sand size sediments cementing the grains together forming unique deposits, known as matrix, opalised sandstone or “concrete” which is a more conglomeratic unit near the base of early Cretaceous sediments.

The many variations in the types of opal depends on a number of factors. In particular, the climate provides alternating wet and dry periods, creating a rising or more importantly a falling water table which concentrates any silica in solution. The silica itself is formed either by volcanic origin or by deep weathering of Cretaceous clay sediments producing both silica and white kaolin often seen associated with the Australian opal fields. Special conditions must also prevail to slow down a falling water table in order to provide the unique situation for the production of its own variety of opal.

The chemical conditions responsible for producing opal are still being researched, however some maintain that there must be acidic conditions at some stage during the process to form silica spheres, possibly created by microbes.

While volcanic-hosted and other types of precious opal are found in Australia, virtually all economic production comes from sediment-hosted deposits associated with the Great Australian Basin. Australia has three major varieties of natural sediment-hosted precious opal – black opals from Lightning Ridge in New South Wales, white opals from South Australia, and Queensland boulder and matrix opal.

The formation of Boulder Opal

The Boulder opal found in Queensland forms in a slightly different method to other types of opal, forming inside an ironstone concretion. The concretion was formed due to ionisation, from sedimentary deposition. By definition, they are ionised concretions of varying hardness with an approximate opal composition of SiO2at 28%, Fe2O3 + AL203 at 68% and H2O at 1% composition.

The opal forms in generally elongated or ellipsoidal ironstone concretions or boulders, from a few centimetres, to up to 3 m across. The boulders may be confined to one or more layers or randomly distributed through the weathered sandstone. Their composition ranges from sandstone types (a rim or crust of ferruginised sandstone surrounding a sandstone core) or ironstone types (composed almost entirely of iron oxides).

The opal occurs as a filling or lining between the concentric layers or in radial or random cracks in the ironstone, or as a kernel in smaller concretions or nuts. (as found at Yowah and Koroit fields, the famous ‘Yowah-nuts’).

Matrix opal is where the opal occurs as a network of veins or infilling of voids or between grains of the host rock (ferruginous sandstone or ironstone). Rare seam or band opal is also found and is typically encased in ironstone.

Pipe opal occurs in pipe-like structures which may be up to several centimetres in diameter within the sandstone and these structures may be hollow or opal-filled. Wood opal is occasionally found replacing woody tissue material.

As opposed to other sedimentary precious opal, boulder opal is attached to the ironstone, and stones are usually cut with the natural ironstone backing intact. Solid opals may be cut from the ironstone material where the opal is of sufficient thickness.

Boulder opals are fashioned to standard shapes and sizes but are also cut in freeform shapes to highlight their individual beauty and to avoid wastage. Magnificent picture stones are also cut but these are mainly of interest to collectors rather than for jewellery use.

Facts about the Great Artesian Basin:

• Is one of the largest freshwater basins in the world
• Contains approximately 8,700 million megalitres of water
• Underlies 22% of Australia
• Covers a total area of 1.7 million km squared
• Supports a population of 200,000
• Underpins $3.5 billion of production annually

Sources:

“Opal in South Australia”, Mines & Energy Resources, SA
“Opal”, Qld Dept. of Mines & Energy
The Australian Gemmologist, Vol 21, #1, 2001. “Geology of Australian Opal Deposits”, L.J. Townsend.
“Lightning Ridge, Walgett & District”, information booklet, p13.
Queensland Boulder Opal Association

How to Cut and Polish Opal

FAQ:  How is opal cutting done? How do I cut rough opal? Where can I learn about cutting opals? How is opal polishing done? How can I polish an opal?

Opal cutting and polishing is a very specialised skill. Rough opal is normally purchased from the opal miners as ‘parcels’ (Bulk quantities of opal in its rough state). Potential buyers sort through the parcels and try to predict the value of stones which can be produced from the rough material.

However there is never any guarantee, as opal cutting can produce very unpredictable outcomes. Once the opal cutter has sorted through the parcel and decided which pieces are worth cutting, a diamond saw is used to cut the rough opal into ‘ rubs’ (opal in the rough shape of a stone). During this process, any excess material, cracks and potch (colourless opal) is cut off, and the piece of opal is cut into a basic stone shape.

Probably the most basic concept which any opal cutter needs is to keep the stone as large as possible, i.e. minimising waste and maximising the end size of the stone.

Each moment of cutting reduces the size of the stone, so control must be exercised.  The second basic concept is that opal can be ‘burned’ or may even crack if subjected to extreme temperatures. For this reason, water must always be used when cutting opal to avoid overheating due to friction.  ‘Burning’ a stone during polishing results in small pits forming on the surface thereby ruining the smooth surface and polish.

After the stone has been cut on the saw by hand, the opal cutter will then normally place the stones on ‘dop sticks’, consisting of nails or lengths of wood dowling, using heated wax to adhere the stone to the end of the stick. This allows a greater degree of control of the stone on the cutting wheel, especially when the stone is small. The wax is softened on a burner to permit the fixing of the stone, which is first adhered with the face of the stone pointing upwards. The face of the stone is decided by the opal cutter, considering which side has the best colour, and the best shape for the stone.

The opal cutter then uses a series of diamond grinding wheels (coarse to fine) to shape and perfect the stone. Importance is placed on removing imperfections, such as sand spots, and removing saw marks and rough spots from previous stages. The face of the stone is shaped into a cabochon (dome shape) and the shape is decided depending on the stone (normally oval). Again, maximising the size of the stone is an important consideration.

The final stage for the face is polishing. Serium Oxide is used as a polishing agent on a felt wheel with water to give the stone a beautiful polish. If the cutter is happy with the shape, and the absence of scratches, grinding marks or imperfections, he removes the stone and sticks it back on the wax with the back facing up.

The back of the stone is cut on the same set of grinding wheels, this time producing a flat bottom for the stone, and an edge which tapers up to the ‘girdle’. The shaping of the girdle is an important and difficult part of cutting, and refers to the point on the side of the stone where the two top & bottom edges meet. This edge is used by jewellers to set the stone underneath the gold, to provide a secure setting.

Boulder opal can be significantly more difficult to work. The opal forms in tiny cavities in the ironstone, therefore the seams of opal that run through the boulder can be of very excellent quality but are very thin veins from .25mm to 20 mm thick. The ironstone is generally left as backing to support the stone.

Occasionally a thick vein is deposited allowing the cutter to cut the opal in cabochon, however frequently the veins are thin and wavy, so the cutter is challenged to cut and polish the piece following the deposition of the opal, resulting in an undulating or baroque surface. Stones are generally cut into freeform shapes, which is dictated by the opal deposition and flaws within the piece.

Ironstone is also significantly harder than opal, (opal is only as hard as glass) which provides another challenge for the opal cutter. Opal will grind much quicker than ironstone, so extra care must be taken when polishing a surface comprised of both materials.

So, now you know how to cut opal! Well, not exactly… this is only a very rough guide, and it takes a lot of practice to cut opal correctly. We recommend that learners get hold of some cheaper rough material to begin with, and to get a feel for the stone. Cutting and polishing opal is a great skill, and it’s also very rewarding to uncover such beautiful colour!

Sources:

• Queensland Boulder Opal Association

FAQ:  What causes the colours in opal? How does opal get its colour? What is potch? Where do opals get their colours? What is the structure of opals? Why does opal have colour?

The colour of an opal is a magnificent thing. Unlike any other gem, opals can display all the colours of the rainbow in an iridescent, moving pattern of red, green, blue, yellow, purple, aqua, pink, and any other colour you can imagine. The pattern and arrangement of the colour which is displayed in an opal can take on many beautiful forms, and the movement of colour across the face of a stone is known as the ‘play of colour’.

This captivating miracle of nature has been admired by people the world over for centuries, and highly sought after for use in jewelry, museums and collectors’ pieces. The opal is arguably the most beautiful of all gems – at the very least it is highly unique and a true treasure of the earth. The very idea that such magnificent colours have been hidden under the earth in darkness since ancient times, and pulled out of the ground to display their opalescence in the light of day, is truly staggering.

But what causes the colors in an opal? What is different about opal that makes the colours dance and play across the face and burn in every colour of the spectrum?

The answer, put simply, is the diffraction of light. Much like a prism, which can refract white light and produce a rainbow effect, opals diffract the white light which is coming from above, displaying those amazing opal colours. To understand how this happens, it’s time for a lesson on the microscopic structure of opals;

The Structure of Opals

Basically, opal is made up of water and silica (the main component in glass). A silica solution forms when silica from under the earth mixes with water. This solution fills voids or is trapped in layers under the earth, and opal begins to form. Learn more about how opal is formed.

Over a long period of time, the solution settles and the water evaporates, allowing the gradual formation of layer upon layer of microscopic silica spheres. The spheres are formed because particles of silica spontaneously adhere to other particles which form around it. These spheres of range in size from 1500 to 3500 angstroms (1 angstrom is 1 ten millionth of 1 millimetre).

Because they are spherical, there are tiny gaps remaining between the spheres (much the same as when marbles are placed together in a container). In these gaps between the stacked spheres, a water and silica solution remains. The spheres in an opal are not only remarkably uniform in size but are packed, in gem quality opal, in a very regular array. It is these tiny spheres and gaps which hold the secret of the opal’s colour. See image, left – An electron-microscope photograph of of the ordered structure in precious opal, showing its light-diffracting spheres.

The Diffraction of Light in Opals

When white light waves enter the top of an opal, they refract and bounce around inside the opal, through all the microscopic spheres and the gaps between the spheres. As the light passes through the spheres and gaps, it diffracts (splits). Like a prism, the opal splits the white light into all the colours of the spectrum, and the light eventually bounces back out the top of the stone, at which point we get an eyeful of beautiful opal colours. The opal is the only known gemstone that is able to naturally diffract light in this way.

You may have noticed that some opals don’t have all the colours of the spectrum. Many opals can only display blue colouring, for example. This is because the diameter and spacing of the spheres controls the colour range of an opal. Getting back to our colour diffraction theory, the size and angle at which light is split determines the colour produced.

Small spheres produce opal of blue colour only (the most common), whereas larger spheres produce red (the rarest colour). When the spheres inside the opal are bigger (about 3500 angstroms diameter) the red or orange colours are produced. At the other end of the scale, at about 1500 angstroms in diameter, the blue end of the spectrum is diffracted. Between these sizes the rest of the colours of the rainbow occur.

Therefore the rarity of the colours (most common to least common) is as follows: blue, green, yellow, orange, and red. Opals which display red can also display all the other colours of the spectrum. Therefore the possible combinations of colours in an opal can be seen as: blue only, blue-green, blue-green-yellow, blue-green-yellow-orange, and finally the full spectrum of blue-green-yellow-orange-red. For this reason, the presence of red in an opal can greatly add to its value, since it is somewhat of a rarity. Opals can also contain aqua and purple as well as the other ‘non-primary’ colours which are produced when two primary colours are combined. (For example, the green and orange between the primary colours of blue, yellow, and red).

It can also be deduced that the light diffraction in the voids is greatest when the sphere size is greatest. Therefore, generally speaking, red is usually the brightest opal color and blue is duller. 

Potch, also known as common opal, is any type of opal which does not display any color. In this case, the silica spheres may be absent, too small, or too irregularly arranged to produce colour. (Opal which does display colour is known as precious opal.) Potch is virtually worthless, although it often serves as an excellent dark backing for black opals which normally have a thin segment of precious opal naturally formed on a potch backing.

If you have seen our online opal catalogue, you will have noticed a number of categories used to describe and classify each stone. This system of offering detailed information about each stone is based on the Australian Opal Ebusiness Association’s (AOEA) Opal Classification Standard, and aims to offer as much information about each stone as possible, allowing you to make an informed decision about your opal.

Clearly there is no substitute for viewing a stone in person, however we believe that our videos and pictures (in which we take meticulous care to represent our stones accurately), combined with this classification system, allows our customers to buy with confidence. Our clients are almost always pleased with their stone once it arrives, since as a general rule a stone is better in real life than in any photograph. For a good detailed run-down on how the value of an opal is determined, please see our article on valuing opals.

Our Classifications Explained:

ID – This is the unique identification number issued to each opal when it is processed.

Category – The preface Solid means that the stone is a natural cut & polished opal which does not have any kind of backing adhered to the stone to enhance the colour (as is the case with the partially fabricated stones – doublets or triplets). Queensland Boulder Opals, even though they have a natural brown ironstone backing which makes the stone darker, are still known as solid opals since this is the natural formation of the stone. Read more about the types of stones.

Black Opal refers to opal which has a dark grey to black body tone, and is generally mined in the Lightning Ridge area of New South Wales. As a general rule, black opal is the most valuable form of opal, since its dark body tone causes the colours to be more vibrant.

Boulder Opal is opal mined in Western Queensland which normally has a natural brown ironstone backing attached to the stone. Boulder opal usually has a very dark body tone and is thus generally the second most valuable form of opal.

Crystal Opal means any kind of opal which has a translucent or transparent quality (i.e. you can see through it). Translucent or transparent stones often have an enhanced clarity of colour, and for this reason it usually increases the value of a stone. The term Crystal Opal normally denotes opal with a very light body tone, however Black Crystal Opal refers to a crystal opal which has a dark body tone.

Semi-Black Opal refers to opal which has a light to medium grey body tone and is therefore not quite dark enough to be called black opal. These opals usually fall within the ‘dark opal’ category in the Body Tone Index. (See diagram further down) Semi black opal is generally found in Lightning Ridge, but is also found in White Cliffs and occasionally South Australia. This can be one of the lesser valuable forms of opal.

White Opal means opal with a white to light body tone, and is also known as milky opal. White opal is found in large quantities in South Australia, and the bulk of it does not have the same vibrancy of colour as found in other forms of opal. For this reason, it is generally one of the least valuable forms of opals. (High quality white opal is available however.)

Setting – In the case of jewelry, this indicates the carat of the gold used, and whether it is White Gold or Yellow Gold.

Weight – This refers to the carat weight of the stone. Five carats equals approximately one gram. The value of an opal is usually determined by calculate a price ‘per carat’ according to the colour and appearance of the stone, and this value is multiplied by the carat weight. When there are multiple stones, the carat weight of all stones combined is given.

Origin – The place in Australia where the stone was mined. See our article on Australia’s opal mining fields for more detailed information on each field.

Dimensions – The dimensions (width and length of the stone facing upwards) measured in millimetres. One inch equals 25.4 millimetres. In the case of a freeshape stone, the measurements are generally given at the widest points of the stone. When there are multiple stones, the dimensions of the largest stone are given.

Thickness – The measurement in millimetres of the stone’s thickness (i.e. looking at the side of the stone). This measurement is taken as close to the centre of the stone as possible. This includes any potch (colourless opal) or ironstone which is naturally attached to the back of the stone. In the case of boulder opal, the actual layer of opal can be less than 1mm thick. Our stones are cut with enough backing on them to support and stabilise the stone and give them a good shape. We never leave extra weight or thickness on the back of a stone to boost its carat weight or value.

Body Tone Index – (See Figure 1, below). This is a device used to classify the darkness of a stone. Generally a darker stone leads to more vibrancy of colour, however it depends on the individual opal. Boulder opals are always listed as having a body tone index of 0 since they cannot be classed in the same system as other opals due to their ironstone backing. Boulder opals generally have a very dark body tone however.

Transparency – Refers to the ‘diaphaneity’ (transparency) of an opal. Opaque means the stone is not transparent. Translucent means the opal has a semi-transparent nature. Transparent means you can see through the stone. This category is used to determine whether a stone has any of the properties of a crystal opal.

Shape – Refers to the shape of the stone. Freeshape means anything which is not in a standard oval shape. Cabochon refers to the dome on the top of the stone. A cabochon can effect the appearance and pattern of a stone – for example, crystal opals often look better with high cabochon, whereas black opals can look better with a low to medium cabochon. This is up to the individual stone however and relies on the skill of the opal cutter to maximise its beauty and pattern. Low Cabochon means it has a flat or hardly any dome. Medium Cabochon means it has a medium dome. High Cabochon means it has a high dome on the surface.

Colours – Lists each colour of the spectrum which is visible in the opal. Generally the most prominent colour is listed first, then the second most prominent colour and so forth. The rarity of colours is as follows – in order of the rarest (most valuable) to the most common (least valuable). Red; Orange; Yellow; Green; Blue. Red is therefore the rarest and most highly sought-after colour in an opal, and therefore fetches the highest price. Unusual colours may also occur, such as purple and aqua which can also enhance the beauty and value of a stone. Read more about how opal displays colours in our opal colour article.

Brightness – This is one of the most important ways in which we determine the value of an opal. There are three brightness ratings – Subdued, Bright, and Brilliant. These categories are quite broad and are intended to give a general indication of a stone’s brilliance. Subdued means the stone falls into this category with the least brightness – (note that it still may be a beautiful stone). Bright means the stone has a good level of brilliance and falls into the middle category. Brilliant means the stone is a real eye-catcher – has excellent brightness and falls into the top category in this classification. Brilliant is obviously the most sought-after and valuable property for a stone as it is a very desirable quality.

Pattern – This is a description of the arrangement of the colours on the face of the stone and how they appear to the eye. The most common pattern is Floral, which we use as a very broad description meaning a random and relatively indistinct pattern of opal colours. Most opals fall into this category.

More valuable patterns include Pinfire (small dots of colour sparkling like stars), Broad Flash (large sections of colour which flash brightly at certain angles), and Rolling Flash (a large section of colour in which a bright flash rolls across a section of the stone as you move it).

Even more valuable patterns include; Ribbon (Almost indescribable – Multiple rolling flashes which line up in different sections moving next to each other and in succession), Flagstone (large distinct blocks of colour), Straw (small and thin multiple lines of colour next to each other), Chinese Writing (thin strokes of colour which look like chinese writing).

The most valuable and rare pattern is Harlequin, in which blocks of colour lie next to each other and are of approximately the same size and shape (like a checkerboard). This pattern is extremely rare and is the legendary in opal circles. Many websites on the internet use the term Harlequin very liberally, so be wary of what you are buying. Traditionally a true Harlequin opal is extremely valuable and rare, and can fetch hundreds of thousands of dollars. In two decades of experience, our opal cutter has only ever seen two true Harlequin opals, just to give you an idea of their rarity.

Notes – This is where any extra description, special characteristics, faults or interesting attributes are mentioned.

Any questions? Don’t hesitate to email us!

Shop our range of ready- made opal engagement rings

FAQ: Where can I find an opal engagement ring? Are opals suitable for engagement rings? Where can I find opal wedding rings? Does Opals Down Under custom make opal engagement rings?

Australian opals, also known as “The Queen of Gems” are one of the most beautiful gemstones in the world. Opals display all the colours of the rainbow in an amazing moving diffracted colour pattern known as the play of colour.

This makes opals very unique and opal engagement rings are becoming increasingly popular amongst people looking for a different and original engagement ring a little different to the standard diamond ring. Opals, unlike diamonds, are genuinely rare – as fast as opals are mined, they are sold. Diamonds are in fact very common, yet prices are kept high by vast stockpiling and strict supply control.

Unlike diamonds however (which are incredibly hard 10/10 on the Mohs scale), opals are a relatively soft gemstone. Opals rank at a 6 1/2 on Mohs scale of mineral hardness. To put this into perspective, opals are just a little harder than glass. This is the most important thing to be aware of when considering an opal for an engagement ring. It is possible by mistreating an opal or treating it roughly, to damage or break the stone. This does not mean opals will break at the drop of a hat, it just means you need to treat them carefully to ensure you enjoy your opal for a lifetime!

When our customers tell us they are looking for an opal engagement ring, we always ensure they are aware of this factor before they start their search. There are a number of ways you can ensure the maximum security and durability of your opal, and you should consult the advice of experts before going ahead and buying an opal ring.

Opals Down Under has made hundreds of customised opal rings, and we’ve got engagement rings down to a fine art. Here are our tips to help you get the best out of your opal ring:

Tips for buying an opal engagement ring

• Pick a rub-over (bezel) setting. We strongly advice this for opal engagement rings, as rub-over settings provide much better protection and security for your opal. A thin bezel of gold follows and covers the edge of the stone, protecting damage from impact, and ensuring the stone stays securely in place. Claw settings are less secure and provide less protection, which means your opal is more vulnerable. 
• Boulder opal is harder wearing. Due to its very hard natural ironstone backing, Queensland boulder opal is more robust and has an advantage over other types of Australian opal. For an opal engagement ring, boulder opal is ideal. Black opals, crystal opals, and white opals are also suitable, but do not have the same hard-wearing quality as boulder opals. Due to their unusual ‘free’ shape, boulder opals also lend themselves to more creativity in design.
• Select a stone with a low cabochon (i.e. dome on top). Opals with a high cabochon are more exposed and vulnerable to impact damage, so if your stone has a flat or low cabochon top, it’s less likely to be damaged.

In summary, opals can make a beautiful lasting engagement ring if you make the right choice and treat the opal with respect. We have made many opal engagement rings for our clients over the years – simply email us your ideas and we’ll promptly draw up some designs for you.

The cost of your opal ring depends on the type of stone and setting you choose, as well as the size of your finger. Please don’t hesitate to contact us if you’d like to talk about having an opal engagement ring custom designed, we’d be more than happy to help. In the meantime, feel free to learn more about opals, or check out our current stock of opal rings.

A guide to purchasing opals.

FAQ : What to look for in an opal – What is a doublet? What is a triplet? How do I buy opals? What are the different types of opals? How can I get value for money when I’m buying an opal?

If you’re not an expert, buying an opal can be a very daunting task. To help you out, we’ve put together this little guide, which will hopefully help you make the right choice for your needs.

Educate Yourself

Read as much as you can about opals so you know what you’re getting. One of the missions of our website is to provide as much information as possible about opals so our customers can educate themselves until they feel satisfied.

Before buying, determine whether you are looking at a doublet, a triplet, or a solid opal. Doublets & triplets consist of a very thin slice of opal, cemented onto a black backing. This causes the stone to be dark & bright in colour (the idea being to replicate the highly valuable black opal). The advantage of buying a doublet or triplet is a lower price (they are much cheaper to produce) – however the disadvantage is they may eventually be destroyed if repeatedly immersed in water. Solid opals are therefore considered much better – they’re 100% the “real thing” and are a quality, long-term investment.

Types of opal

Black opals, boulder opals, white opals and crystal opals – these are all different types of opals, the difference being that they are found in different parts of Australia, and each have very different appearances.

In summary;

• Black opals are the ‘Rolls Royce’ of opals, and often have a certain price attachment associated with their status and rarity. Black opals are generally considered to be the best in the world due to their dark body tone.
• Boulder opals are the much lesser known cousin of the black opal, but they can have equally stunning colour. The opal forms in thin veins on an ironstone backing (hence the dark colour), therefore the price is generally much less per carat due to the ironstone content of the stone. Be wary of people selling boulder opal at a price ‘per carat’, leaving a heavy ironstone back on the stone. This is a sneaky way of boosting the price of the stone. Boulder opals are the most ‘hardy’ of all opals due to their very hard ironstone backing.
• White opals have a ‘milky’ white body tone, and are much more common. The white body tone often causes the colour to be less bright, however by the same token, high quality white opals can be captivating.
• Crystal opals – this is any type of opal with a translucent / transparent quality. This quality can add value to a stone when combined with good colour.

Selecting an opal

Pick a stone that appeals to you! Each stone has an individual personality, much like people, so nobody can tell you what your opal should look like. Red on black is most valuable, but if you like blue, go for a blue stone!

Consider what you’re going to be using the stone for. Shape and size is an important factor when considering the setting for jewellery. If you are buying a high quality stone, consider matching it with a high quality setting.

Consider the brilliance – A brilliant stone is good, no matter the colour or body tone, but you’ll pay more. Stones classed as ‘bright’ are still beautiful, and even subdued stones can still be amazing.

Colour values – red is the most valuable, followed by orange, yellow, green, and then blue being the most common.

Certificates of Authenticity – always ask for a signed certificate of authenticity with your opal. Not only is it good for insurance purposes, and re-sale value, you are also making the dealer accountable.

Learn how opals are valued – read our article on how opal is valued. Educate yourself on the general principles of opal valuation and compare stones. There is no ‘formula’ for figuring out the value of a stone, although people have tried and are still trying to formalise this process. There is no substitute for years of experience mining, cutting, and valuing stones. Buy from someone who has a good reputation, preferably someone who cuts or mines the stones themselves.

Cracks and faults – Any opal vendor worth their salt will clearly state any inclusions or faults within a stone which are visible to the naked eye. Natural inclusions and faults are OK, but don’t buy a stone with cracks. If you are inspecting the stone in person, make sure it’s dry, then hold it up against a lamp to inspect it for cracks. Be careful not to mistake natural formation lines in opal for cracks (eventually you will be able to tell the difference). A cracked stone is virtually worthless. The person you are buying the stone from has an obligation to make you aware of any cracks or faults in the stone before you purchase it.

GST & prices – GST (Goods and Services Tax) is a value-added tax of 10% added on most goods and services transactions in Australia. Prices on our website are shown in both inclusive and exclusive GST prices. If you are an overseas customer, you do not need to pay this tax. Exported goods are tax-free and not subject to Australia’s GST. Opals Down Under passes this benefit onto our international customers and internet purchases shipped overseas are accordingly tax-free. Customers who reside in Australia however will be charged this tax at the rate of ten per cent. Please select the correct tax bracket when submitting your order.

Buying opals over the internet – it’s understandable that some people will be concerned about doing business over the internet. Here are some of the questions we’ve received over the years:

• How can I be sure I’m getting what I see in the photos?

Good question. Opal photography is by no means an exact science, and everybody has a different method, camera, conditions, and experience when it comes to photographing opals. Irresponsible sellers looking to make a quick buck can easily enhance their pictures to make the stones look better, so you need to trust who you’re dealing with.

In our experience, there’s no way we can 100% accurately portray the beauty of a natural Australian opal on a computer screen, but we think we get pretty close. Each item has several photos and a short video to give you the best possible idea of what you are buying. We are obsessive about taking photos which accurately represent our stones, and take our photography very seriously. If we tried to rip people off, we’d have been out of business many years ago. As a safety net for you, we provide a 100% money back guarantee – if the opal arrives and you’re not happy for any reason, just send it back for a full refund. End of story. You have complete protection from receiving a product which does not meet your expectations.

• Do I really want to give my credit card details to someone I have never met?

Truth be known, there will always be a certain amount of trust required for conducting business over the internet. We continue to build on our forty-five year reputation in the opal industry by doing business the only way we know how – openly & honestly. Our integrity also has the right technology to back it up – all credit card details are processed through a secure, high-level encrypted SSL server. Your credit card details are not transmitted via email, and kept highly confidential.

I hope this guide has been of some use to you. Please don’t hesitate to contact us if you have any further questions.

FAQ :  What is the history of opal? Are opals bad luck? Is opal bad luck? Why and when did superstition begin to surround opal?

Opal… the Bad Luck Stone?

For many years, the opal has tried to shake off rumours and wives tales about the stone bringing bad luck. Perpetuated by folk lore, mistaken identity, superstitions, family tales and disgruntled diamond traders, the opal has had a pretty tough life. As we entered the age of reason and science, this belief has somewhat fallen by the wayside, but a glimmer of the superstition still survives today. Of course, like any unprovable theory, you’ll have to make up your own mind, but we’ve got our feet planted firmly in the non-believers camp. After all, we’ve owned and loved opals for over forty-five years and they’ve brought us nothing but good luck!

The Luck of the Opal: A History

The folklore connected with crystals, gems, and precious stones is as old as it is varied. Much of this tradition dates back to the beginnings of civilization, when jewelry was worn not only as adornment but also as protection against occult forces and human foolishness. Amethyst, for example, was thought to sober drunks, quell sexual passion, and cure baldness. Aquamarine was believed to protect seafarers, while emeralds increased fertility and intelligence, imparted prophetic ability, and other wild talents. Rubies provided defense against every kind of misfortune, made hostile neighbors friendly, and promoted one’s stature in the community.

The opal’s nasty reputation however has troubled folklorists for centuries. Fantastic legends have grown up around this harmless stone, cautionary tales designed to discourage those who might otherwise find themselves mortally attracted by its fiery brilliance. To this day, the odd prejudice against opals remains alive and well in some corners of the world, especially in the backwaters of southern Europe and the Middle East, where jewellers won’t carry opals and customers won’t buy them.

Throughout history, while many stones were prized for their positive magical qualities, others were denounced as vessels of evil. No gem was more vilified than the poor opal. Witches and sorcerers supposedly used black opals to increase their own magical powers or to focus them like laser beams on people they wanted to harm. Medieval Europeans dreaded the opal because of its resemblance to “the Evil Eye,” and its superficial likeness to the optical organs of cats, toads, snakes, and other common creatures with hellish affiliations.

An opal completely contaminated with evil were believed capable of maiming or even killing a person foolish enough to wear or own it. Tales alleging to prove this are few in number, but the belief persists nevertheless, like those old but curiously tenacious admonitions about walking under ladders, stepping on a crack in the sidewalk, or allowing a black cat to dart across one’s path. Popular superstitions such as these will be with us always, but however fanciful they may be, most have prosaic origins.

The early years – the “good luck” opal

The Romans established opal as a precious gemstone, obtaining their supplies from traders in the Middle East. Opals from this era are thought to have come from Cernowitz, a mountainous region in what was at that time Hungary , but now Slovakia. However early Romans believed the source was India, an incorrect belief promoted by traders in order to protect their interests.

They believed the opal was a combination of the beauty of all precious stones, and it is well documented in Roman history that Caesars gave their wives opal for good luck. They ranked opal second only to emeralds, and carried opal as a good luck charm or talisman because it was believed that like the rainbow, opal brought its owner good fortune. In the days when Rome spread her legions across Europe and Africa, a Roman Senator by the name of Nonius opted for exile rather than sell his valuable opal to Marc Antony who wanted to give it to his famous lover Cleopatra.

In fact, in Roman times, the gem was carried as a good luck charm of talisman, as it was believed that the gem, like the rainbow, brought its owner good fortune. To the Romans, it was considered to be a token of hope and purity.  It was also referred to as the “Cupid Stone” because it suggested the clear complexion of the god of love. The early Greeks believed the opal bestowed powers of foresight and prophecy upon its owner, while in Arabian folklore, it is said that the stone fell from heaven in flashes of lightning. The Oriental traditions referred to them as “the anchor of hope”. Lucky opal – the stone of hope, the birthstone of October.

Special Powers

Early races credited opal with magical qualities and traditionally, opal was said to aid its wearer in seeing limitless possibilities. It was believed to clarify by amplifying and mirroring feelings, buried emotions and desires. It was also thought to lessen inhibitions and promote spontaneity.

In the 7th Century it was believed that opals possessed magical properties, and centuries later Shakespeare was attributed with the description of opal as “that miracle and queen of gems”. Eastern peoples also dealt very heavily in this precious stone, which was believed to bring luck and to enhance psychic abilities.

However, the entire time the Hungarian mines supplied Europe with opal, including a stone for the crown of a Roman Emperor, superstitions circulated attributing evil powers and maladies to the colourful stone. In the eleventh century, Bishop Marbode of Rennes wrote of opal, “…Yet ’tis the guardian of the thievish race; It gifts the bearer with acutest sight; But clouds all other eyes with thickest night.” This is thought to be based on the idea that opal granted its bearer with invisibility, therefore it was a talisman for thieves, spies and robbers!

Opals were also thought to have teleportation powers. A piece of opal jewelry might suddenly disappear from some obvious place, only to turn up weeks or months later somewhere unexpected. Of course, forgetfulness might also be to blame.

Fear and loathing of the opal did not discourage the development of a counter folklore which cast the stone as a symbol of hope, innocence, and purity. The Arabs of Mohammed’s time were quite enamored of the gem, and were convinced they were carried to earth on bolts of lightning. European writers and poets of the Middle Ages also sang the opal’s praises, claiming it had curative effect on bad eyes, protected children from predatory animals, banished evil, and made entertainments, friendships, and romances much more intense and enjoyable. Fair-haired girls in Germany and Scandinavia were encouraged to wear opal pins in their hair, as they were thought to add magical luster to their golden locks and protect them from freezing rain, wind, and other vicissitudes of the Nordic climate.

In the Middle Ages, the opal was known as the “eye stone” due to a belief that it was vital to good eyesight. Blonde women were known to wear necklaces of opal in order to protect their hair from losing its color. Some cultures thought the effect of the opal on sight could render the wearer invisible. Opals were set in the Crown jewels of France and Napoleon presented his Empress Josephine a magnificent red opal containing brilliant red flashes called “The Burning of Troy.”

The “Evil Eye”

Medieval Europeans shunned opal because of its likeness to the eyes of several “evil” animals, such as cats. Fear of the Evil Eye, common to cultures the world over, was and remains especially acute in the Mediterranean. Simply defined, the term signifies a covetous or malicious glance meant to bring harm. Witches were thought to possess this awful power in great abundance, though common people with unrealized magical talents could also wield it, albeit unconsciously. The Eye did its stuff directly and indirectly. It could strike its intended victim sick or dead on the spot, or kill family members, blight crops, sicken livestock, or summon a storm with the muscle to level a house, a village, or an entire town.

The Evil Eye’s association with the opal probably originated in Elizabethan England. There the stones were called “ophals,” a shortening of the word ophthalmos, which referred to the human eye. The Evil Eye was accepted as fact in 16th Century Britain, as was belief in omens and auguries. In the minds of superstitious Elizabethans, the occult link between ophals and ophthalmos was both obvious and ominous.

Fear of the Eye crossed the Atlantic with European settlers. In Puritan New England, colonists wore heart-shaped pendants with prayers inside to protect themselves from the godless gaze of Satan’s servants – witches, sorcerers, and magic workers who could be found in every forest clearing, every abandoned barn, and under every bed.

Ironically, they had it all wrong. The word opal had actually descended from the Roman “opalus,” an ancestor of the modern opal that was thought to heal the blind and make a person invisible to his enemies. Opalus was among the most virtuous of stones. To the Romans, who in their own way were even more superstitious than the Elizabethans, it was certainly no kin to the Evil Eye.

Plague, death & disaster

During the late 18th and 19th centuries opal fell out of favour, as it was associated with pestilence, famine and the fall of monarchies. Opal was also tied to the Black Plague, an affliction that struck in the middle of the 14th Century, ultimately eradicating more than a third of Europe’s population and much more in neighboring territories. During the decimation of Europe by the Black Death, it was rumoured that an opal worn by a patient was aflame with colour right up to the point of death, and then lost its brilliance after the wearer died. As the plague put Europe under siege, desperate people searched for a scapegoat. They found several in the persons of Jews, heretics, and, of course, the much-maligned opal.

Queen Victoria, however, did much to reverse the unfounded bad press. Queen Victoria became a lover of opal, kept a fine personal collection, and wore opals throughout her reign.

“The year 1348, an astrological Martial sub-cycle, saw Venice assailed by destructive earthquakes, tidal waves and the Plague,” wrote Isidore Kozminsky in The Magic and Science of Jewels and Stones. “The epidemic in a few months carried off two-thirds of the population of the city sparing neither rich nor poor, young nor old. It is said that at this time the opal was a favorite gem with Italian jewelers, being much used in their work. It is further said that opals worn by those stricken became suddenly brilliant and that the luster entirely departed with the death of the wearer. Story further tells that the opal then became an object of dread and was associated with the death of the victim.”

Many centuries later, a Spanish king would sully the opal’s already sordid reputation further still. In the late 19th Century, Alfonzo XII fell madly in love with a beautiful aristocrat named the Comtesse de Castiglione. The Comtesse reciprocated the King’s affection, but months before the pair were to wed the faithless Alfonzo married another woman, the Princess Mercedes. Vowing to get even, the Comtesse sent the couple a wedding present in the form of a magnificent opal set in a huge ring of the purest gold. The princess was immediately smitten by the gift and insisted that her husband slip it on her finger. He obliged, and two months later the princess mysteriously died.

After the funeral Alfonzo gave the ring to his grandmother, Queen Christina, who almost immediately thereafter also expired. After that the ring passed to Alfonzo’s sister, the Infanta Maria del Pilar. Maria died as well, apparently victim to the same weird illness that had taken the other two women. The ring was up for grabs yet again, and when Alfonzo’s sister-in-law expressed an interest, he let her have it with the usual result.

Deeply depressed by then, the King decided to end it all by slipping the ring on his own finger, just as Cleopatra had embraced the asp to terminate her own misery. In little over a month, the ring did to Alfonzo what the snake had done to the Egyptian Queen. The ring was finally attached to a gold chain and strung around the neck of a statue of the patron saint of Madrid, the Virgin of Alumdena. That put an end to the incredible chain of tragic circumstances, but was the gem really responsible for the calamities besetting this royal family? According to Kozminsky, it seems pretty unlikely.

“At this time it must be remembered that cholera was raging through Spain,” he writes in The Magic and Science of Jewels and Stones. “Over 100,000 people died of it during the summer and autumn of 1885. It attacked all classes from the palace of the king to the hut of the peasant, some accounts giving the death estimate at 50 percent of the population. It would be as obviously ridiculous to hold the opal responsible for this scourge as it was to do so in the previously noted plague at Venice. All that may be said is that in this case the opal was not a talisman of good for King Alfonzo XII of Spain and to those who received it from his hand, and that in the philosophy of sympathetic attraction and repulsion man, stones, metals and all natural objects come under the same law.”

Anne of Geierstein

The saddest opal saga is the oft-repeated misconception in the last of Sir Walter Scott’s novels, Anne of Geierstein (1829), which irrevocably linked opal to misfortune. Having not read the third volume, the public jumped to the conclusion that the heroine has been bewitched, that her magic opal discolours when touched by holy water, and that she dies as a result. On carefully examining the texts, Si Frazier, writing in Lapidary Journal, found all three accusations false. The opal, which actually belonged to Anne’s exotic grandmother, turns out to have turned pale as a warning to its owner against poisoning (which was the actual cause of her grandmother’s death). Even so, this single work plunged opal prices to half in just one year and crippled the European opal market for decades.

George F. Kunz, author of The Curious Lore of Precious Stones, says, “There can be little doubt that much of the modern superstition regarding the supposed unlucky quality of the opal owes its origin to a careless reading of Sir Walter Scott’s novel, ‘Anne of Geierstein’. The wonderful tale… contains nothing to indicate that Scott really meant to represent opal as unlucky.”

Unlucky jewellers

Another contributing factor to opal’s bad reputation may be the fact that opals are a relatively fragile gemstone. Opals are a soft gemstone compared to diamonds, and can be broken if mis-treated or treated roughly. This may have contributed to an overall perception of opal as “bad luck”, since anybody would be heartbroken to lose a precious beautiful opal or family heirloom.

“A possible explanation of the superstitious dread that opal used to excite some time ago may be found in the fact that lapidaries and gem-setters to whom opals were entrusted were sometimes so unfortunate as to fracture them in the process of cutting or setting,” wrote George Frederick Kunz in The Curious Lore of Precious Stones.

“This was frequently due to no fault on the part of the cutters or setters, but was owing to the natural brittleness of the opal. As such workmen are responsible to the owners for any injury to the gems, they would soon acquire a prejudice against opals, and would come to regard them as unlucky stones. Very widespread superstitions have no more foundation than this, for the original cause, sometimes quite a rational one, is soon lost sight of and popular fantasy suggests something entirely different and better calculated to appeal to the imagination.”

One royal opal did bring terrible misfortune to the hapless goldsmith who broke it during setting. The unforgiving Louis XI ordered his hands cut off! It’s no surprise that few of his colleagues thereafter had anything good to tell buyers about opal, therefore some blame opal’s maligned reputation on the difficulty that lapidaries had with cutting and setting them.

Bitter traders

Some maintain that diamond merchants of the mid 19th and early 20th centuries saw the amazing attributes of opal and realised it was going to be a serious threat to their livelihood. When high quality Australian opal appeared on the market in the 1890’s, it is understood that diamond cartels actively spread the false rumour that opal was unlucky and seriously damaged the reputation of opals.

Opal, with its stunning play of colour, was increasing in popularity and could represent a threat to the lucrative diamond trade now that it was being mined commercially. The story goes that jealous diamond traders spread the belief that opals are bad luck to protect themselves and give opals a bad reputation. Some of the rumours stuck and became the ‘old wives’ tales which are still repeated today.

The lucky stone

Isidore Kozminsky in the 1922 edition of his book The Magic and Science of Jewels and Stones states that “perhaps against no other gem has the bigotry of superstitious ignorance so prevailed as against the wonderful opal.”

He also cites several historical references to the talismanic qualities of opal including the story of a French baron who resided in London, who owned an opal that had been in the family since the twelfth century. In 1908 he took the opal to the London Pavilion where a soothsayer told him that the opal would bring him good fortune and that he was about to inherit £500,000! The London newspaper “Evening News” reported that within a few days the soothsayers’ prediction had come true, it also stated that the ancient opal had a feint inscription in old Spanish, which translated to the words “Good Luck”.

Another anecdote tells the tale of a rich city financier who took his ‘opal ring’ to a jeweller: he wanted to sell it because of the ill luck it had brought him. A tale of misfortune was recounted. As a result of wearing the ring, his wife had fallen ill, a condition that also affected his son, and he encountered among many other troubles financial difficulties and ill health. The jeweller, however, merely smiled and showed him that the stone in the ring was not an opal but a moonstone. Only his imagination had endowed the opal ring with such unpleasant properties.

There are many reports of opal bringing people luck, including the many opal miners who have made their fortunes and have lived long and prosperous lives. A well known piece of history comes from the Lightning Ridge Historical Society. Mick McCormack, a young opal miner at Lightning Ridge, rode off on his bike when war was declared and went to enlist, simply saying to his friends “I’ll be back”. A lifetime went by and a very old man was in the Lightning Ridge Hotel showing a piece of opal that he had mined and carried with him through the Great War. At the time he was showing it a buyer offered him 1500 pounds Australian for the stone. The old man said, “1500 quid? Not on your life, mate – I wouldn’t accept fifteen thousand quid. I carried this opal through the war with me and I remember one time when I thought it was my last day on earth. Men were killed all around me. Night time, it was, and there was the flashes of the guns and the shells bursting all around us. My hair was standing up and I was sweating. I was really frightened. I had the opal in my tunic pocket. I took it out and looked at it and something …sort of …calmed me down. I looked at the opal in my hand and I thought , some day, I’ve got to go back to the Ridge. And I’ll get back! And I’ll take this stone back to where it came from. No mate, money can’t buy this stone.” A couple of old miners finally realised who this old man was. They had grown up with him as kids and it was their old mate Mick who had been true to his word and had finally brought his stone home.

Some people believe that opal is bad luck… however, we at Opals Down Under believe it’s bad luck if you don’t have one! One person who would back us up is Harry Brukarz, who owned an opal shop at the corner of Martin Place and Castlereagh Street, Sydney. Harry won numerous lottery prizes in the 1940’s and 1950’s, and attributed his lottery winnings to “the luck of the opal”. The major $120,000 (60,000 pound) prize he counted among his winnings represented a tidy fortune in itself. 

Despite all of this and more, the bad rap against opals has stuck through the ages. This can be partially explained by human nature. For most people, a bad opal will always have more appeal than a good one, a cursed opal more fascination than an opal that brings good luck, wards off wicked influences, or cures. We humans love a mystery, and the darker the mystery, the better we like it.

Sources :

• “Opals”, by Fred Ward, Gem Book Publishers, 1997.
• “Australian Precious Opal”, Andrew Cody, 1991.
• “Fatal Attraction”, by D. Douglas Graham, Colored Stone magazine, September / October 2001.

FAQ : How can I tell if an opal is real? What is Gilson opal? What are synthetic opals? How can I tell if an opal is synthetic? What is synthetic opal? How can I identify opals? Is my opal real?

HOW TO TELL IF AN OPAL IS REAL

FAQ : How can I tell if an opal is real? What is Gilson opal? What are synthetic opals? How can I tell if an opal is synthetic? What is synthetic opal? How can I identify opals? Is my opal real?

SYNTHETIC OPAL, DOUBLETS & TRIPLETS

Have you ever pondered if you’re getting what you paid for? Well, hold onto your curiosity hats, because synthetic opals are a real thing. Plus, there’s a bunch of partially man-made options like triplets and doublets out there. In this article, we’re here to give you the inside scoop on how to be crystal clear about what exactly you’re bringing home. (For even more opal insights, hop over to our article on opal types where we dive deeper into the world of solids, doublets, and triplets.)

First things first, check if the stone boasts a white body tone or has that transparent charm. If it does, chances are high that it’s a genuine solid, and you’re probably looking at a splendid white or crystal opal. Now, for doublets and triplets, they’re all about that dark body tone because they rock a black artificial backing.

Sneaky Layers and Backs

Take a peek at the opal from the side. See distinct visible ‘layers’? You might be dealing with a doublet or triplet – not a full-on solid opal. In the doublet world, one of those layers is a thin slice of opal attached to a dark backing. But wait, there’s more! A triplet brings a third layer to the party, a clear, domed layer that sits right on top of the opal.

Now, turn your gaze to the back of the opal. Does it remind you of hard black or grey plastic? Triplets often cosy up to a backing of black plastic, glass, or vitrolite. Doublets, they’re a tad trickier to pin down. They might flaunt a natural potch or ironstone backing (that’s the brown boulder opal’s host rock). Here’s the real giveaway: look again at the side of the stone. Check if the ‘join’ between the opal and the backing is perfectly flat, creating a straight line around it. Most real solid opals have a little quirk in this zone – they’re curvy or bumpy, showing off their natural formation. Man-made stones? They’re all about the perfect flatness because those two sections have been meticulously glued together. But hey, if your opal’s already set in jewellery with the back and sides undercover, that’s a trickier call even for an expert.

Glassy Tops and Beyond

Is the top of the opal giving off a ‘glassy’ vibe? Triplets tend to wear a cap of hard clear plastic or quartz, giving their top a different reflective flair compared to natural opal. And here’s a tip: if you can glimpse through the opal’s top from the side, there’s a good chance it’s a triplet.

Crucial Knowledge Before Your Purchase

Before you dive into opal ownership, take a little schooling. Familiarise yourself with the look of real opal and put it side by side with your potential purchase. There’ve been tales of folks slipping coloured tinsel or foil beneath clear plastic to mimic opal’s magic. Sneaky, right?

Decoding Synthetic Solid Opals

Now, let’s talk synthetic solid opal. They’re sneaky to spot, unless you’re an expert or have clocked in plenty of experience. The pattern can be a giveaway – lab-made opals like Gilson opal rock bright colours in neat patches all over. Often, the pattern seems a tad ‘too perfect,’ almost like it’s striking a pose. Sometimes, they even flaunt a ‘snakeskin’ pattern. Not sure yet? Don’t fret. Take it over to a gemologist or an opal pro for some insights.

When Clouds Gather

Keep an eye out for cloudiness. If your opal turns cloudy after hanging around for a while, it might just be a triplet or doublet. This cloud show happens when those layers have taken a dip in water over the long haul, causing the glue to wear down and give water a ticket to the party.

Oh, and before you go, a quick note: triplets, doublets, and synthetic opals can be awesome wallet-friendly stand-ins for natural opals. Just remember to keep your gem senses sharp so you don’t find yourself overcharged or led down the garden path.

Synthetic (Gilson) Opal

View our latest stock of Solid Natural Australian Opals now.

Most common words are below:

• Agitator – or ‘agi’ for short; a modified cement mixer used to wash and tumble opal dirt. Usually set up adjacent to a dam for water supply.
• Amorphous – a word meaning “without form”, applied to gems and minerals that have no definite or orderly arrangement of atoms or crystal structure and have no external crystal structure.
• Artesian Basin – a large body of underground water that covers some 1,750,000 square kilometres or around 676,250 square miles in the inland of Australia and occurs in many other places in the world. A huge source of water by way of bores or wells in the arid areas.
• Automatic hoist – a machine which can be activated from underground to pull a bucket up the mine shaft and tip its content out; used to carry opal dirt up and dump it into a truck.
• Ballroom – a term used to describe a large cavity in an opal mine where the opal dirt has been removed in the search for opal. These ballrooms can be quite large.
• Bar – a descriptive term for the way the actual opal colour forms in a nobby or piece of seam opal, usually referred to as “the colour bar”.
• Black opal – the most rare and valuable type of opal. Due to its iron oxide and carbon content, black opal has a dark body tone, which gives greater intensity to the gem colour. The word ‘black’ doesn’t refer to the colours displayed by the opal – black opal comes in every colour of the rainbow. Learn more about black opals.
• Blow – a formation resembling a cylindrical ‘tube’ varying in diameter from a few inches to many feet and found in the actual opal ‘level’, sometimes containing some opal fragments and made up of a whitish sandy material which is often very hard. Thought to be steam or pressure vents millions of years ago.
• Blower – a machine like a giant vacuum cleaner, used to suck opal dirt from underground into a pipe, up the shaft and into a waiting truck. A more recent invention than the automatic hoist.  A blower can remove massive quantities of opal dirt.
• Body tone – Opal is rated on a body tone scale from dark to light. N1-N4 is “black opal”, then N5-N6 is “semi black” and N7-N9 is “light”.
• Bogger – a small vehicle with a tipping scoop on the front, used in some mines to move opal dirt from the mine face to the mine shaft for transport up to the truck.
• Boulder opal – mined in Queensland, this gem forms naturally on a dark brown ironstone. Boulder opals often show colour just as well and sometimes better than black opals. Learn more about boulder opals.
• Bummy – a slang term used on the opal fields to describe a stone which has been cut with large or excessive backs on them.
• Buyer – someone who buys opal from miners, runners, or other buyers.
• Cabochon – the domed or convex top which is shaped and polished on a finished gemstone. i.e. a non-faceted surface which is rounded and smooth all over. This technique is used in place of faceting in opal cutting.
• Calibrate – to cut a stone to a regulated standard size, usually by template and the use of vernier calipers.
• Carat – a unit of weight used to measure opals and other gemstones. One carat equals one fifth of a gram.
• China Hat – a formation of rough opal nobby with a peaked centre, thought to be an ancient lily centre which has fossilised into opal.
• Cleave or Cleavage – the ability of a gemstone or mineral to break in a certain direction usually because of its crystal structure. In opal, the cleavage plane is totally irregular and somewhat haphazard. The veins of opal in boulder opal are sometimes cleaved apart to expose the opal.
• Common Opal – This term describes all opal that doesn’t have a play of colour, but rather is one or other of the base colours, e.g. white, grey, black – i.e. potch.
• Coocoran – A fairly large basin that, during flood times, becomes a lake some 7 kilometres long and 3 kilometres wide. More importantly it is the name for the largest opal field of late in the Lightning Ridge area. Used to describe the large group of opal mining fields around and beyond the lake.
• Crystal opal – any kind of opal that is transparent or translucent. Learn more about crystal opal.
• Diaphaneity – the property of being transparent or translucent, often applied to opals when referring to crystal opals.
• Digger – a hydraulic machine with a digging claw, used underground to mine opal. The miner stands at the controls of the digger while it is operating.
• Doublet – Fine slices of white or crystal opal placed on top of a dark backing, making it look like the much rarer black opal. Learn more about opal doublets.
• Dopping – the technique of adhering a stone to a stick in order to handle it better during the cutting and finishing processes, using a specially designed wax.
• Drill – these days many miners buy or hire a large drill to explore prospective opal-bearing ground. The drill is used to bore holes up to nine inches diameter, bringing earth and rock to the surface to be inspected for indications of opal.
• Drive – the name used to describe a tunnel dug for the extrication of ‘opal dirt’, usually situated directly below the roof to a depth of about six feet.
• Fire opal – this can refer to a couple of different things. Mexican Fire Opal is the only opal which is technically referred to ‘fire opal’ within the opal industry. However, the term ‘fire opal’ has also been used to describe any opal with a brilliant flash of ‘fire colours’ – i.e. red / orange colour. This is not a term which is generally used in Australia to describe opal. The term is also occasionally used less accurately to describe black opals with red colouring.
• Fossils – a fossil is a remnant of what was, either whole or in part, but usually replaced by some other element, for example opal, which produces fossilised opal.
• Gouge – a term used by miners to describe the action of gently picking at the face to find opal as opposed to actual digging. Gouging is done when checking for trace or when opal has been seen, so as to get it out quickly rather than waiting for the processing to be done.
• Hoist – A mechanical device pioneered in Lightning Ridge that takes the dirt from the mine to the surface automatically.
• Inclusion – Any material that has formed internally in opal, such as matrix, sand or even mud, and occasionally Gypsum, also known as dendrite.
• Ironstone – Rock that has a rusty redish brown appearance and is composed of iron oxide, mostly a conglomerate. In boulder opal the actual opal is in or around this material, and is cut leaving the boulder host rock on the back of the stone.
• Level – The name given to that strata where opal could be potentially found – commonly called opal dirt.
• Mohs’ Scale – The internationally recognised scale for measuring hardness in gems and minerals.
• Mullock or Mullock Heap – A term used to describe the piles of opal dirt lying on the surface on all the fields.
• Nobby – a naturally lump-shaped piece of opal. The nobby form of opal is only found at Lightning Ridge.
• Opal – An amorphous non-crystalline gem mineral solidified from gelatinous or liquid silica deposited in cracks and cavities left by decaying vegetation, wood, crustaceans and bones millions of years before. Very valuable in its ‘black’ forms and containing a reasonable content of water. Chemical symbol: SiO2 plus H2 O. In higher grades of opal the water content can be as high as 10%. Refractive Index of 1.38 – 1.60 and a hardness of between 5.5 to 6.5 on Mohs’ scale. Learn more about opal.
• Opal carving – a specialised method of opal cutting, used to conserve gem opal and to produce uniquely-shaped gemstones with freeform shapes and undulating surfaces.
• Opal cutter – a skilled person who cuts rough or rubbed opal into cut and polished gemstones.
• Opal dirt – claystones in which opal is found.
• Opalised or Opalized fossil – opal which has filled a void in the earth caused by decomposed objects, in the shape of teeth, bones, shells, plants, etc. to form an opal fossil.
• Orientation – a term associated with opal cutting used to descibe the skill of making the absolute best out of a rough piece of opal in terms of colour, shape pattern, etc. The art of getting the best out of a stone.
• Potch – common or colourless opal – a form of non-precious opal that doesn’t contain gem colour.
• Prop – an upright log used to support the roof of an underground mine.
• Ratter – a person despised on the opal fields. A thief who steals opal from a mine, an agitator or a pile of tailings.
• Rough – opal that hasn’t yet been touched by cutting equipment.
• Rub – opal that has been roughly ground down or ‘rubbed’ by cutting machinery to remove gross impurities and establish a preliminary shape.
• Runner – someone who sells opal to buyers on behalf of the owners of the opal, usually on a commission basis.
• Saw – In terms of opal cutting, an automated diamond saw, comprising a circular blade with the outside edge coated with diamond. Used with water for lubrication and to avoid overheating of the opal.
• Seam – a horizontal layer of opal in the ground. Opal is often found by miners by following a ‘seam’. Very thin seam is known as ‘trace’.
• Triplet – A partially man-made stone, triplets are a paper-thin slice of opal with a dark backing, and quartz crystal capping to magnify the colour. The stone is made to imitate the much rarer and valuable black opals. Learn more about triplets.
• White opal – opal with a white or light body tone, normally found in South Australia. Learn more about white opals.
• Windlass – a winch used to haul opal dirt up out of the mine. These days, most miners use an automatic hoist or blower for this purpose.

Sources :

• “Lightning Ridge, Walgett & District” information leaflet, p. 7.
• “Black Opal: A comprehensive guide to cutting and orientation”, by Greg Pardey, GP Creations, 1999.

FAQ :  How is opal valued? What makes a good opal? What are the different patterns in opal? What faults can opal have that detract from its value? What is the play-of-colour? What should I look for in a good opal? How are opals valued? Why are some opals more expensive than others?

The value of an opal depends on many factors. The type of opal, body tone, brilliance, pattern, colour bar thickness, the play of colour, and faults all play important roles in determining the value.

Other important factors include the quality of the cut & polish, and the size of the stone. When being valued, opal is carefully examined and given a price ‘per carat’. The overall carat size of the stone will then determine the price of the opal.

Opal class

First of all, it is essential to identify the type of opal which is being valued. An opal doublet or triplet can be worth considerably less than a solid opal. Doublets and triplets are an ‘assembled’ stone which only contains a very thin slice of natural opal and are therefore generally much less valuable.

Body Tone

Body tone is one of the most important factors in the classification and valuation of opals. Body tone refers to the background or the ‘underlying colour’ of the opal, which ranges from black through dark to light. Generally opals with a black or dark body tone are more valuable than those with a white, light, or crystal body tone, because a stone with a darker body tone tends to display colours more vibrantly.

Above – AOGIA 1-9 body tone scale.

Black opal is the most prized opal and may realise prices over AUD $15,000 a carat. Boulder opals also have a dark body tone. White opals have a light body tone and are generally the least valuable form of opal.

The term crystal opal refers to the ‘diaphaneity’ (transparency) of an opal, not its crystal structure, and is defined as any type of opal which is translucent to transparent. (See image, below) Some crystal opal displays colour so intense, so dark, that the opal is referred to as ‘black crystal opal.’

Above – Black Opal, Semi-black Opal, Boulder Opal, Crystal Opal

The play of colour

The phenomenon known as the “play-of-colour” is the brilliant range of the full spectrum of colours caused by the diffraction of white light by the internal structure of orderly arrayed spheres of silica. Red (fire) opal is generally more valuable than a mainly green opal which, in turn, is more valuable than a stone showing only blue colour. Nature does not produce a red colour as often as it does a blue or green. Red colouring is caused by larger microscopic silica spheres, whereas blue is caused by the more common small spheres.

Brilliance

Brilliance refers to the brightness and clarity of the colours displayed by opal, when the stone is viewed face-up. This ranges from brilliant , bright , to subdued or dull.

Pattern

The pattern of coloured segments, forming the play-of-colour of a precious opal, is unique to every individual opal. The distinctiveness and colour displayed by these segments determines the quality of the pattern of an opal.

Excellent patterns include;

• Harlequin, large sections of colour in which each colour segment is roughly the same size and shape, like a mosaic or chequerboard. A true harlequin pattern is extremely rare and highly sought after.
• Flagstone, large sections of colour with straight edges, in a random pattern
• Ribbon, narrow, parallel cascading lines of rolling colour
• Straw, random thin strips of overlapping colour
• Chinese Writing, thin strips of overlapping colour which resemble Chinese characters
• Picture stones, the intriguingly unique patterns of ‘novelty’ or ‘picture’ stones, which resemble an object, landscape, animal, person, etc.

Good patterns include;

• Floral – a random pattern of colour with good spread
• Rolling Flash – large sections of colour which roll across the stone as it turns
• Broad Flash – large sections of colour which flash as the stone turns
• Pinfire – tiny points or specks of colour

Poor patterns are indistinct, and are characterised by patterns featuring Moss and Grass.

Above patterns – left to right, Harlequin, Flagstone,  Chinese Writing, Broad Flash, Straw, and Floral. ( Photos by Len Cram).

Colour bar

The thickness of the colour bar in opal is relative to the overall size and shape of the individual stone. Boulder opal typically has a very thin colour bar due to the way the opal is geologically formed. This should be taken into account when valuing the stone, however makes little difference to its appearance once set in jewellery.

Faults

Faults which can detract from the value of a finished opal are many and varied. A crack in the face can render almost worthless an opal that otherwise might have been worth a considerable amount per cart. Crazing, i.e. many small cracks in the opal’s face will also relegate the stone to worthless.

Sand and various other minerals can be found as inclusions in and/or under the colour bar, and in the potch of opals. Sand/sandstone inclusions in the potch (on the underside of the opal) will have no effect on the value of the opal.

Other faults include potch lines, webbing, (grey lines) and windows (sections devoid or lacking in colour). The consistency of colours and pattern when viewed from different directions also has an influence – when a stone “won’t face”, the colour only shows through on certain angles and otherwise has little colour. The visibility of potch or brown ironstone on the surface of the stone will also lead to a drop in value.

Conclusion

All the above factors are taken into account when valuing opal, however there is no substitute for experience. Truth be known, there is no standardised or set method for valuing opals, as each opal is extremely unique in terms of pattern, brightness, and colouring (unlike diamonds, which can be more accurately valued according to a set chart of colours, clarity, faults, etc.) Always ask for a certificate of valuation / authenticity with your opal, and get a second opinion from an experienced valuer if you are concerned about the value of your stone.

Sources :

• “Opal in South Australia”, Mines & Energy Resources, SA
• “Opal”, Qld Dept. of Mines & Energy
• The Australian Gemmologist, Vol21, #7, “Classification of Type 1 Natural Opal”, Joseph Schellnegger.

FAQ :  How is opal mining done? What is noodling? How are opals mined? How is opal mined? What is open-cut mining? How are opals processed?

Opal is one of the few minerals which can be extracted economically by a miner working alone. The simplest form of mining, carried out in the early days of opal mining, is by shaft sinking with a pick and shovel. A shaft is sunk straight down until some promising “opal dirt” is discovered. The miner would then branch out sideways, following the “level” of opal. Driving along the level is carried out with picks and explosives. A handpick or screwdriver is used to delicately extract any opal found, due to the frailty of the stone. Most mining was a two-man operation, one man in the hole and another up top to wind the windlass and haul out the dirt.

Most shafts are now sunk by Calweld-type drills which are used to sink vertical holes about one metre in diameter using an auger bucket. Waste material, or mullock, from the shafts and drives was originally lifted in buckets by hand windlass, but power winches or automatic bucket tippers are now used.

Of course, sinking a hole in recognised opal country offers no certainty of finding what is sought. More than sixty separate ‘fields’ have been worked at Lightning Ridge alone, and each of them has waxed and waned according to what was found. Following “seam opal” on a field such as The Grawin means first locating a seam of the glassy gray “potch” in hopes that at some spot, the potch will suddenly take on the qualities of gem opal. These underground ribbons bend, turn, dip to impossible depths, or simply disappear according to the pressures exerted on the earth long ago. Tantalising hints of those prehistoric times sometimes are uncovered in the form of opalised sea shells or opalised fossils from the days of the dinosaurs.

There has been a rapid increase in the use of mining machines since the 1970s. Tunneling machines with revolving cutting heads and small underground front-end loaders (boggers) have been introduced to streamline opal mining and dramatically increase productivity. Miners soon saw the benefits of technology – drilling test shafts to gauge their chances before beginning serious excavation, using jackhammers instead of pickaxes, blasting with dynamite, or bringing in the bulldozers. Bulldozers are employed to remove overburden and expose the level where it is shallow. Spotters follow behind watching for traces of opal, and any seam found is then worked over by handpick.

Of course, all of these labour savers sometimes end in bitter tears, when the opal is spotted only after it has been shattered. They also increase the cost of equipment and operation.

In Queensland, the majority of mines worked in recent years are large open-cut operations. Overburden is stripped from zones of ironstone boulder concretions. Boulders are carefully removed from the ground for processing. Heavy equipment has been used to open up most areas of old workings. At Yowah, underground methods are still applied with success. Shafts are sunk until a prospective layer is intersected. The layer is then explored by the driving of tunnels. Usually at least two shafts are sunk and connected by drives to allow circulation of air. In areas of underground mining, miners utilise ‘light’ electrical machinery driven by portable generators.

If the boulders show any evidence of opalisation, they are first removed from the mined ground and collected for later inspection for opal content, and sorted in readiness for sale as rough, or for further processing. For boulder opal, some of the ironstone is left attached as a natural backing, producing natural doublets. Other stones are cut from the ironstone matrix containing opal.

The Australian export market for opals has been in decline in recent years, but this trend is likely to be turned around as production increases from existing and new deposits. Australia exports most of its opal to Hong Kong, Taiwan, Japan, USA and Europe.

As most old diggings have now been largely worked out or reworked by open-cut methods, exploration to find new prospects has commenced over known opal bearing country. Well-resourced exploration companies have become involved and are applying more systematic and extensive exploration techniques on a regional scale in the search for new deposits. Positive results have been reported, which should lead to further exploration and new mines.

In addition to the traditional opal fields, exploration for opal has been undertaken in the Hebel-Dirranbandi area near the Queensland – New South Wales border where there is a 70 km northern extension of the Cretaceous Griman Creek Formation, which hosts the Lightning Ridge opal field.

Both shaft and open-cut mining takes place at Lightning Ridge, although shaft-mining is more common due to the way opals on this famous field were formed. “Ridge” opal is encased in rounded formations known as “nobbies”… but not all nobbies contain opal. At Andamooka, “seam opal” is the object of the miner’s search.

Near whatever water is available, an array of concrete mixer trucks is a common site – used to ‘agitate’ (wash and sluice) the opal-bearing material like gigantic washing machines. “Blowers” at some locations suck the opal dirt into trucks at topside, which haul the dirt to the “agitator” for sluicing.

Noodling

Many locals make a living out of searching through heaps of discarded mullock for pieces of precious opal. Noodling machines in which mullock is passed by conveyor under an ultra-violet light in a darkened enclosure are also used. Many people enjoy partaking in this activity during visits to the opal fields, and some do it for a living.

Sources:

• “Opal in South Australia”, Mines & Energy Resources, SA
• “Opal”, Qld Dept. of Mines & Energy
• “Make your own Luck with Opal”, Jewellery World, June 2000.