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Myth: Opals need to be soaked in water occasionally to prevent cracking.

Fact: Australian Opal is non-porous and therefore impervious – it cannot soak up water, oil, or anything else. The water content in an opal is determined during the formation of the stone, with water molecules locked into tiny voids within the opal’s crystalline silicon structure. Soaking your opal in water will do nothing to increase the life of your opal. However, wetting an already cracked stone will temporarily hide the fault, a fact which may have contributed to prolonging this myth. It’s important to note that opals should never be cleaned in an ultrasonic cleaner, as the extreme vibrations may cause the opal to crack. However, Hyrdrophane Opal (usually sourced from Ethiopa) is now gaining in popularity, but we do not cut or stock it.

Myth: Opals are extremely fragile and will break very easily.

Fact: It’s true that opals are more fragile than most gemstones, however they’re not as fragile as some people imagine. Opals are about the same hardness as glass, so imagine you’re wearing a piece of glass and you’ll get the idea. Avoid heavy manual labour, moving furniture, sport, gardening or any other vigorous activity where your opal might impact with hard surfaces and your opal will enjoy a long and happy life. With a little common sense it’s easy to take care of opals. Boulder opals and opals with a low cabochon are sturdier and less easy to damage.

Myth: Opals need to be rubbed with oil (baby oil or olive oil) or glycerin occasionally to prevent cracking.

Fact: Rubbing your opal with oil will do nothing more than make your opal oily. Australian Opals are non-porous and do not soak up liquids, therefore baby oil will not increase the life of your opal.

Myth: Opals are unstable and prone to cracking.

Fact: Most opals are extremely stable and never crack. Stable opals have a water content of approximately 3 to 10 per cent, and any unstable material will normally crack soon after being mined. By the time the opal travels from the mines, and is processed, cut and polished, any unstable material is usually identified and weeded out.

Myth: Water damages solid opals. Never clean your opal with water or get your opal wet. The opal will expand and crack.

Fact: Solid opals cannot be damaged by getting wet. Most Australian precious opals contain around 5-6% water, and immersing a solid opal in water will do no damage whatsoever. However, doublet and triplet opals (non-solid, partially man-made layered stones) can be damaged by prolonged exposure to water. Water penetration can eventually cause the glue to deteriorate and the layers to separate, causing the opal to take on a foggy, grey, or cloudy appearance. This fact is the origin of the ‘never get your opal wet’ misconception.

Myth: Black opals are completely black. (like onyx)

Fact: If an opal was completely black, it would also be completely worthless. Black opals display a myriad of rainbow colours, and the more colourful the better. ‘Black’ simply refers to the comparatively dark body tone of the stone when compared to the milky body tone of white opals. Top quality black opals can be more valuable per carat than diamonds.

Myth: Strong light can cause an opal to dry out.

Fact: Strong light will only make your opal shine brighter. However, be wary of very hot lights as extreme heat can cause opals to expand and crack.

Myth: Rubbing oil or detergent on your opal will damage or discolour it.

Fact: Oils, detergents and many other common household items will not damage your opal. However, we recommend steering clear of harsh chemicals and cleaning products such as bleach, chlorine, oven cleaner and other strong chemicals. Whilst these may not necessarily damage your stone, it’s best to be on the safe side and treat your opal with respect. It’s important to note also that doublet and triplet opals should never be immersed in any liquid, as prolonged exposure can lead to separation of the stone’s layers.

Myth: Rubbing a stone with glycerin, rubbing it with toothpaste, or soaking it in water will revive a stone’s lustre when it needs polishing, or prevent a stonefrom losing its lustre.

Fact: Wetting a stone will temporarily make it look better, but there’s no other way to restore an old stone’s lustre apart from having it professionally polished. Solid opals may eventually need to be re-polished after a number of years due to tiny scratches on the surface removing the fine polished appearance of the stone. The stone will need to be polished by an experienced opal cutter using professional equipment.

Myth: Taking your opal to high altitudes in a plane will cause it to crack.

High altitudes will not affect your opal. The only major things that can damage your opal are impact, extreme fluctuations in heat (e.g. placing your opal over a flame) or extremely low humidy for long periods. Extreme variations in heat cause the opal to expand and contract, causing cracks or crazing.

Myth: Soaking an opal in rose water will enhance the colour.

Fact: Wetting your opal in any kind of water will make it look better. This is only temporary. The only true way to maximise the colour of a stone is to have it professionally polished. Rose water has no special properties for enhancing opals.

Myth: Opals are bad luck.

Fact: The ‘bad luck’ myth is the result of centuries of misinformation, superstition, wives’ tales, and jealous diamond traders spreading rumours. Opal has also been considered a good luck talisman and lucky charm throughout the ages, and has been prized by many civilisations. Find out more about the ‘bad luck’ opal myth.

Myth: Triplet opals are opals with three colours.

The name ‘triplet’ refers to the number of layers in the stone, not the number of colours. Triplets consist of a thin slice of opal glued to a black backing, which is designed to imitate black opals. The triplets have a third layer of crystal, glass, or quartz capping to round off the stone and give it a cabochon. ‘Doublets’, on the other hand, consist of two layers – a thin layer of opal and a black backing, with no capping. Read more about doublets and triplets.

Myth: The light causing the opal’s colours comes from within the stone.

Fact: Opal’s colours are caused by the reflection and diffraction of white light which enters the top of the stone. The light bounces around inside the tiny microscopic silica spheres within the stone, causing the diffraction of light and the ‘prism’ or rainbow effect which we all know and love. Learn more about opal’s colours.

Myth: Warming an opal in your hand will enhance its brightness.

Fact: The heat of an opal has no effect on its display of colour.

Myth: Putting your opal out in a lightning storm will improve the colour.

Fact: Considering the personal danger associated with this, it’s not a very good idea. Lightning has nothing to do with opal colours. This perception may come from the ancient Arabian belief that opals were cast down in lightning storms.

If there are any other myths you can think of, or something you’ve heard about which you’re not sure is true, please don’t hesitate to email us and we’ll investigate it and include it in this list!

FAQ :  How do I take care of opals? What is the best way of caring for opal? What is a doublet? What is a triplet? How do I clean my opal? What happens if I get my opal wet?

Because we love opal, we like to educate our customers on how best to care for their opals, so they can enjoy the beauty of this individual and precious gemstone for many years to come. Please take a few moments to read this guide, and don’t hesitate to email us if you have any questions.

Doublets, Triplets, & Solid Opal

Taking care of opal is easy. All it takes is a little bit of common sense and knowledge about opal. Before deciding how to best care for your opal you need to be aware of the type of opal you have;

• Doublets – Doublet opals consist of two layers, a thin slice of opal and a black backing. The slice of opal is cemented to the backing in order to enhance the colour.
• Triplets – Similar to doublets, triplets also include a third transparent layer on the top (quartz or glass) to protect the opal and give it a rounder shape.
• Solid Opal – Natural solid opal which has only been cut and polished.

Caring for your Opal

Solid Opals – Opal is a soft stone, approximately the same hardness as glass (around 6.5 on Moh’s hardness scale), so it is important to treat your opal carefully in order to avoid damaging it. Remove your opal jewellery if there is a chance it will be scratched or broken (i.e. working in the garden, moving furniture, etc.)

Many people believe solid opals can be damaged by water – however, this only applies to doublets and triplets. Solid opals are fine in water. In fact, most precious opals contain about 5-6% water. As a result, opal may crack if subjected to very dry conditions or rapid changes in temperature. Try to avoid very high temperatures or low humidity extremes, such as boiling water or zero humidity bank vaults.

Doublets & Triplets – Caring for doublets or triplets is a little different to caring for solid opals. Because doublets and triplets consist of multiple layers glued together, prolonged exposure to water will eventually cause lifting between the layers and the infiltration of water. A doublet or triplet will take on a ‘foggy’ or grey appearance if this happens. This does not mean your opal will be ruined if you wear it in the shower once, or are caught in the rain. It takes prolonged exposure to cause water damage to a doublet or triplet.

Cleaning Your Opal

Solid opal should be cleaned gently with mild detergent in warm water and a soft toothbrush or cloth. Avoid bleach, chemicals and cleaners. Doublets & triplets may be wiped with a damp soft cloth and mild detergent, but should never be soaked or immersed.

Never allow anyone to clean your opal in an ultrasonic cleaner, as the intense vibrations may cause cracking in a solid opal, and water penetration in a doublet or triplet.

If your stone loses its shine or becomes scratched, bring it back to an opal cutter. After years of wear, small scratches and scuff marks cause an opal to lose its shiny polish and become dull looking. Professional polishing can bring new life to an opal which has become dull or scratched, and we can also check for claw damage and ensure the security of the setting.

Storing Opals

If you need to store your opal away for a period of time, simply place it in a padded cloth bag for protection and store it away. For longer storage periods, place your opal in cotton wool with a few drops of water, then into a sealed plastic bag just to be safe. The water is not intended to soak into the stone (as opal is impervious) but will prevent water coming out of the stone if it is exposed to very low humidity environments (for example, zero humidity storage safes).

We hope this guide has been helpful to you, feel free to contact us if you have any further questions… Take care!

FAQ: What is a crystal opal? What colour are crystal opals? Where are crystal opals mined? What is the value of a crystal opal?

Appearance

The term “crystal opal” refers to any kind of opal (i.e. black opal, white opal, semi-black opal) which has a transparent, translucent, or semi-translucent body. This is also referred to as the “diaphaneity” of a stone. If light is able to pass through the stone, or you can see through an opal, then you are probably looking at a crystal opal. Crystal opals can display any colour of the spectrum in a beautiful play of colour.

However, boulder opals which have a layer of translucent opal are not referred to as crystal opals because of their opaque ironstone backing.

The translucence of a crystal opal often gives it a greater clarity and vibrancy of colour than opaque stones. Pale coloured crystal opals (white crystal opals) are generally more valuable than opaque white opals, and ‘black crystal opals’ can often have more beautiful colour than opaque black opals.

Crystal opals are generally cut in a standard oval shape if possible, however if the nature of the stone dictates, sometimes a freeform or teardrop shape is cut in order to maximise the size and carat weight of the stone. Crystal opals are also cut with a high cabochon if possible as it enhances the appearance of the colour.

Examples of Crystal Opal

Value

Top quality crystal opal may fetch prices of up to AUD $2,500 per carat for a gem quality stone. The clarity and transparency of a crystal opal often enhances the appearance of the colour and therefore gives the stone a higher value than a standard opaque stone. Read more about valuation of opals.

Origin

Crystal opals are mined in South Australia and New South Wales, in the same places where black opals and white opals are found. White Cliffs in New South Wales is well known for yielding good quantities of crystal opal. Find out more about these places in our article on the Australian opal fields.

View our full current stock of Australian crystal opals

Shop our range of Unset White & Crystal Opals

FAQ: What is a white opal? What colour are white opals? Where are white opals mined? What is the value of a white opal?

Appearance

Also known as ‘milk’ or ‘milky’ opals, Australian white opals are distinguished by their pale white or light body tone, indicated in the below chart under “light opal”. As with any kind of opal, white opals can display any colour of the spectrum in a beautiful play of colour.

White opals are much more plentiful and common than other kinds of opal like black opal and boulder opal. Often white opals will have white potch (colourless opal) left on the back of the stone, however sometimes the entire stone will consist of colourful opal.

Because of their pale body tone, white opals generally have less vibrant colour than boulder opals and black opals. They do not have the advantage of having a dark or black background which enhances the stone and makes the opal colour stand out.

Examples of White Opal

Value

By comparison, white opals are the least valuable form of opal. This is partially due to the fact that they are the most common form of opal, but also due to the lack of darkness in the stone which leads to the more vibrant colour in boulder opals and black opals. Opals with a very white body tone also tend to have very pale colour. However, good quality white opal can be incredibly beautiful, and may fetch prices up to AUD $200 per carat. There are many factors including brightness and pattern which determine the overal value of opal. Read more in our article on the value of opal.

A Word on Crystal Opal

Crystal opal refers to any kind of opal which is partially or fully transparent or translucent. However, there is a fine line between white opal and crystal opal. Sometimes there is only a mild or medium translucence which may lead to the opal being classified as either a white opal or a crystal opal, or even a “white crystal opal”. Even some of the photos in the above examples are partially translucent and could be classified as white crystal opals.

When a white opal is partially translucent, it often enhances the clarity and vibrancy of the colour, and thus the value of the stone. Therefore a white opal which has some of the properties of a crystal opal will often have a higher value. More information about crystal opals is available in our crystal opal article.

Origin

White opals are found in South Australia in the major opal fields of Coober Pedy, Andamooka, and Mintabie. Find out more about these places in our article on the Australian opal fields.

View our full current stock of Australian white opals

Shop our range of Unset Boulder Opals

FAQ: What is a boulder opal? What colour are boulder opals? Where are boulder opals mined? What is the value of a boulder opal?

Appearance

Australian Boulder opals are the second most valuable type of opal (following black opal). Boulder opals are easily distinguished by their layer of solid brown ironstone left on the back of the stone. Boulder opals, as the name suggests, are mined from large ironstone boulders under the ground. Thin veins of colourful opal forms in cracks and fissures in these boulders. Because these veins of colour are so thin, opal cutters need to leave the ironstone on the back of the opal to form a full sized stone. The thin layer of opal in boulder opals can display any colour of the spectrum in a beautiful play of colour.

Although the ironstone layer providing the backing to boulder opals may appear similar to doublets upon first inspection, the formation is completely natural. The following photographs show a boulder opal from the front, back, and side:

Due to the dark backing provided by the ironstone, boulder opals generally have a dark body tone which leads to a vibrancy of colour similar to that found in black opals. Sometimes the ironstone is visible on the surface of the stone, which leads to a spotted or motley appearance, and thus reduces the value of the stone. A ‘clean faced’ boulder opal, in which a whole bar of colour is visible on the surface of the stone, is much more desirable and valuable than a surface displaying ironstone spots.

The thinness of the bar of colour in boulder opals means that a high cabochoned surface is extremely rare. Boulder opals usually have a flat surface or an undulating surface. Boulder opals are almost always cut in a freeform shape for this reason, to maximise the size of the stone.

Examples of Boulder Opal

Value

Valuing boulder opal per carat is not generally accepted in the industry due to the large component of ironstone present in the stone. However, to give a rough indication, top quality boulder opal may fetch prices of up to AUD $3,500 per carat for a gem quality stone. A clean faced stone with no ironstone spots is generally more valuable than a spotted stone. Read more about valuation of opals.

Origin

Boulder opals are found only in the state of Queensland, Australia. Major opal fields in this area include Quilpie and Winton. Find out more about these places in our article about the Australian opal fields.

View our full current stock of Australian boulder opals

Shop our range of Black Opals

FAQ: What is a black opal? What colour are black opals? Where are black opals mined? What makes a black opal black? What is a semi-black opal? How are black opals valued? How much is a black opal worth?

Appearance

Australian black opals are the most valuable and widely known type of opal. Black opal is characterised by a dark body tone which can range from dark grey to jet black. (See the following chart). However this refers only to the general body tone of the stone, and is not related to the rainbow or spectral colours present in the opal. Some people expect a black opal to be completely black (in which case it would be completely worthless).

Unlike ordinary opals, black opals have carbon and iron oxide trace elements present, which cause the unusual darkness of the stone. Because of their dark body tone, the rainbow colours in a black opal stand out much better than lighter opals.

This vibrancy of colour makes black opal the most valuable form of all opals. Often a black opal will have a natural layer of potch (colourless opal) left on the back of the stone, which can give the stone an extra darkness and vibrancy of colour. The darker this potch backing is, the darker the body tone, which usually makes for greater vibrancy of colour and a higher value black opal. This is the principle upon which doublets and triplets are based, which are an imitation of solid black opals.

Black opals are generally cut into an oval shape, however this depends on the natural shape of the stone. Sometimes black opals are cut into freeform or teardrop shapes in order to maximise the size and carat weight of the stone. Black opals are normally cut with a low cabochon, due to the opal colour bar often being much thinner in black opal than in white or crystal opals. If the colour bar in an opal is thin, it is impossible to create a domed surface.

Examples of Black Opal

Value

By comparison, black opals are the most valuable form of opal – due to their dark body tone and the resulting vibrant play of colour. Top of the range gem quality black opal can fetch prices up to AUD $15,000 per carat. However, just because an opal is black doesn’t make it valuable. There are many factors including brightness and pattern which determine the overal value of opal. Read more in our article on the value of opal.

Origin

Black opals are mostly mined in Lightning Ridge, in northern New South Wales. Lightning Ridge is famous for the black opal and hundreds of millions of dollars worth of black opals have been found there. In 2008, the black opal was named as the ‘gemstone emblem’ for New South Wales. Black opals have also been found at Mintabie in South Australia.

View our full current stock of Australian black opals

Embarking on a journey through the captivating world of gemstones, we delve into the exquisite allure of semi-black opals. These remarkable gems, also known as dark opals, hold a place of high regard among the treasures of the Earth. With a play-of-colour that seems to hold the secrets of the universe, semi-black opals have captured the fascination of gem enthusiasts worldwide.

The Elegance of Semi-Black Opals

Semi-black opals are a subset of opals that possess a distinctive depth and richness in their colour spectrum. While not completely black, their body colour ranges from dark grey to charcoal, creating a canvas that intensifies the mesmerising play-of-colour that opals are renowned for. The contrast between the dark background and the vibrant flashes of colour within semi-black opals gives them a unique and enchanting allure.

Discovering the Play-of-Color

At the heart of the allure of semi-black opals lies their remarkable play-of-colour. This phenomenon is a result of the interaction of light with the silica spheres present in the gemstone’s structure. As light passes through these spheres, it diffracts into a spectrum of colours, creating a dance of hues that shifts with every movement. The deep, dark background of semi-black opals serves as a dramatic backdrop to this captivating interplay of colours, enhancing their visual impact.

Origins and Rarity

Semi-black opals are predominantly found in the Lightning Ridge region of New South Wales, Australia. This region is celebrated for producing some of the most exquisite and valuable opals in the world. The rarity of semi-black opals is attributed to the unique geological conditions that led to their formation. The combination of precious opal and the dark body colour is a rarity, making semi-black opals highly sought after by collectors and connoisseurs.

The Craftsmanship of Semi-Black Opals

These gems are often cut and polished into various shapes to accentuate their play-of-colour and maximise their visual appeal. From cabochons to intricate faceted cuts, artisans use their expertise to showcase the unique beauty of each semi-black opal. Jewellery designers and collectors alike treasure these gems for their ability to transform into captivating centrepieces that radiate a mystique all their own.

Appreciating Semi-Black Opals: A Unique Gem Experience

Appreciating the allure of semi-black opals is an experience like no other. Their dark, mysterious background contrasts with the vibrant colours that burst forth, creating a visual spectacle that captures the imagination. Whether set in elegant jewellery pieces or displayed as collectible specimens, semi-black opals remain a testament to the natural beauty and wonder that the Earth holds within its depths.

In the realm of gemstones, semi-black opals stand as a testament to the Earth’s artistic prowess, delivering a symphony of colour and contrast that leaves a lasting impression. Their rarity, beauty, and captivating play-of-colour make semi-black opals a prized treasure that continues to dazzle and inspire.

Examples of Semi-Black Opal

Current black opal stock

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

FAQ :  What are the different types of opals? What is Black Opal? What is Crystal Opal? What is Boulder Opal? What is White Opal? What is the difference between the types of opals? What are the different types of opal? What is a doublet? What is a triplet? ‘What is synthetic opal? What is imitation opal?

Black Opal – Black opal is characterised by a dark body tone causing brightness of colour which is unmatched by lighter opals. Black Opals are usually mined in Lightning Ridge, New South Wales, and are the most famous, and sought-after type of opal. The term ‘black opal’ does not mean that the stone is completely black (a common mistake), it simply means the stone has a dark body tone in comparison to a white opal. Learn more about black opals.

White Opal – Also known as ‘milky opal’, white opal features light white body tones, and is mined in South Australia. White opal is more common and because of its body tone, generally does not show the colour as well as black opal. Nevertheless, white opals can still be absolutely magnificent in colour if a good quality stone is found. Learn more about white opals.

Boulder Opal – Boulder opal forms on ironstone boulders in Queensland. This type of opal is often cut with the ironstone left on the back, as the opal seam is usually quite thin. Leaving the ironstone on the back means that boulder opal can be very dark and beautiful in colour. The opal forms within the cavities of the boulders in both vertical and horizontal cracks. Boulders vary in shape and size, from as small as a pea, to as big as a family car. Boulder Opal has a tendency to cleave; when cleaved the “split” leaves two faces of opal, with a naturally polished face. Learn more about boulder opals.

Crystal Opal – Crystal opal is any of the above kind of opal which has a transparent or semi-transparent body tone – i.e. you can see through the stone. Crystal opal can have a dark or light body tone, leading to the terms “black crystal opal” and “white crystal opal”.   Learn more about crystal opals.

‘Fire Opal’ – Many people ask us about ‘fire opal’ so I thought I’d include this one. Fire opal is a term not commonly used within Australia but is quite common amongst Americans. Technically, the main type of opal known as ‘fire opal’ is Mexican Fire Opal, mined in Mexico, which usually has a distinct orange colouring. However, the term has been used to describe any Australian kinds of opal (normally a black opal shows it best) which displays a significant amount of red colouring. Red of course is the rarest colour, so these are quite valuable.  Recent discoveries in Western Australia have unearthed an Australian form of ‘Fire Opal’ – an exothermic type of opal.

Matrix opal – 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). Matrix comprises precious opaline silica as an infilling of pore spaces in silty claystone or ironstone. It generally shows fine pinfire colour in the natural state.

Andamooka matrix opal may be enhanced by soaking the specimen in a sugar solution and then boiling in acid to deposit carbon in the available pore spaces, resulting in a dark background.

Natural oulder opal matrix is another kind of matrix opal, found at Yowah in Queensland, which in its natural state consists of brown ironstone with small deposits of opal interspersed. This kind of opal is not treated.

Yowah nuts – Found in the far South Western mines at Yowah in Queensland, Yowah nuts are ironstone concretions resembling ‘nuts’ which contain precious opal in their centre. Upon cracking or slicing the Yowah nut, the precious opal is revealed.

Welo Opal – an Ethiopian form of opal, which can produce rich colour. This material is known as hydrophane opal, as it is a porous gem, which can absorb moisture (over several hours) and cause the Welo Opal to change appearance.  ‘Dewatering’ of the opal can take anywhere between a few days to a few weeks to occur. Ethiopian Opals can have durability issues due its hydrophane property (the absorbtion of water can possibly cause cracking). Only a fairly recent discovery (2008).

Synthetic or Man-made Stones

Synthetic opal – Opaline silica produced in the laboratory and having a similar structure to that of precious opal. The most well-known form of synthetic opal is Gilson Opal, and you can learn more about identifying this type of opal in our synthetic opal article.

The following differences can be seen between natural and synthetic opal;

• Synthetic opals generally show brighter colours, and colour patches are often larger than in natural opals.
• Colour grain boundaries are generally highly irregular in synthetic opal.
• Within each colour grain in synthetic opal there are numerous sub-grains that produce a distinctive snakeskin pattern.
• Synthetic material generally shows a more ordered array of colours since artificial material does not duplicate the intricate pattern of natural opal.

Imitation opal   – A material such as coloured tinsel set in clear plastic or epoxy resin. (These imitations are virtually worthless and not very convincing to a trained eye).

Doublets & Triplets – Doublets and triplets are partially man-made stones, consisting of only a paper-thin slice of opal cemented to a black backing. Triplets have, in addition to this, a clear quartz or glass capping over the top to magnify the colour, protect the stone, and give it a cabochon (domed) appearance. The idea of doublets and triplets is to imitate valuable black opals at a fraction of the cost.

The following diagrams demonstrate the differences between doublets, triplets, and solid opals;

Solid (cabochon) – Most cutters prefer to produce the opal as a solid cut    ‘en cabochon’ if the gem is sufficiently thick. The opal is left in its natural state and simply shaped and polished on the cutter’s wheel.

Doublet – A thin veneer of opal may show enhanced colour with a dark backing of either black or grey silica material, or a thin slice of common opal cemented to the back of the opal with epoxy resin.

Triplet – A slice of quartz may be used to cap the thin opal veneer to protect it from abrasion. This produces a three-tiered gemstone known as a triplet, which can often display brilliant colours. It is a cheaper method of presentation and can enhance the appearance of the opal.

Doublets and triplets are a good affordable substitute for solid black opals, however their disadvantage is their susceptibility to water penetration. Due to the fact that the layers are attached with glue, a doublet or triplet may become water-logged if immersed in water repeatedly. If this happens, the stone will take on a ‘foggy’ appearance.

Sources:

• “Opal in South Australia”, Mines & Energy Resources, SA
• “Opal”, Qld Dept. of Mines & Energy
• Queensland Boulder Opal Association
• Geology.com

What is opal? Where does opal form? What causes the colours in opal? What is potch? How does opal form?

Opal, a precious gemstone of exceptional allure, holds a prominent place in the world of minerals. But what exactly is opal, and where does it originate? Found predominantly in Australia, opal proudly stands alongside diamonds, rubies, sapphires, emeralds, and pearls as one of the six globally recognized precious gemstones. Australia takes the lead, contributing over 90% of the world’s precious opal supply and proudly designating opal as its national gemstone.

Varieties of Opals: What Sets Them Apart?

Delving deeper into opals, you’ll discover a world of variety. Precious opal and common opal, or potch, are two main categories. But what distinguishes these opal varieties? Precious opals are renowned for their captivating play-of-colour, a rarity that enchants onlookers. In contrast, common opal lacks this play-of-colour and appears less vibrant. Commonly known as potch, it is abundant worldwide. When precious opal intertwines with common opal, it takes on the name potch. Astoundingly, around 95% of mined opals belong to the common or potch category, reflecting a single hue such as white, grey, or black – primarily used as backing for doublets or triplets. Merely about 5% showcase colours, with only 0.25% boasting substantial value.

The Science Behind Opal’s Magic: How Does It Work?

The scientific makeup of opal, referred to as SiO2·nH2O, unveils the secrets behind its enchanting play-of-colour. Comprising hydrated silicon dioxide, a fusion of silica and water, opal’s appearance spans from colourless to dark grey and black. Yet, opal’s true enchantment arises from its play-of-colour, a dance of light within minuscule silica spheres embedded within the opal’s structure. This intricate interplay gives rise to a breathtaking kaleidoscope of rainbow hues, transforming as you change your viewing angle.

Decoding Opal’s Nature: What Defines It?

Opal, a crystalline gem mineral, takes form through the solidification of gelatinous or liquid silica within cracks and voids, often created by decaying organic matter, wood, crustaceans, and bones. Its highest value resides in its “black” forms, embodying a significant water content. Represented by SiO2 plus H2O, opals can encompass up to 10% water content, boasting a refractive index that ranges from 1.38 to 1.60. On the Mohs’ scale, opals register a hardness of 5.5 to 6.5.

The Saga of Precious Opal: How Does It Emerge?

“Precious opal” signifies opaline silica displaying an enchanting play-of-colour. Australian opals, often termed “sedimentary opal,” primarily reside within sedimentary rocks of the Mesozoic Great Artesian Basin. Typically containing 5-6% water, these opals are composed of tiny, well-ordered silica spheres. Their hardness, ranging from 5.5 to 6.5 on the Mohs’ scale, aligns closely with that of glass.

The Birth of Opal: How Does It Form?

Opal’s formation is a captivating journey, beginning with the fusion of silicon dioxide and water. As water infiltrates sandstone, it collects minuscule silica particles. Millions of years ago, this solution seeped into crevices in both sedimentary and volcanic regions across inland Australia. Over millennia, deposition sculpted the opal’s destiny – approximately a centimetre every five million years at a depth of forty metres. Over 1 to 2 million years, solidification ensued, intertwined with shifting climates. The opal’s narrative spans soft phases before eventual solidification.

Opal’s Chromatic Symphony: What Creates Its Colours?

As the solution infused with silica deposited and water content lessened, silica particles clustered to form spheres within the gel. These spheres fused, crafting structures of amorphous silica ranging from 1500 to 3500 angstroms. Like marbles nestled together, they left delicate voids. This meticulous arrangement turned opal into an optical diffraction grating, refracting visible light into its full spectrum of colours. Sphere size dictated the emitted hue, with larger spheres yielding red or orange, and smaller ones radiating blue.

Valuing Opal: How Is Its Worth Determined?

The value of each opal is a masterpiece woven from its distinct traits: body tone, play-of-colour, brilliance, pattern, type and size. Amid the opal expanse, individuality reigns supreme, with each gem reflecting a unique symphony of traits that defines its worth.

Embark on an opal odyssey, where nature’s marvels intertwine with scientific wonders, beckoning you to unravel the captivating beauty of these gemstones.

Click here to download the pdf of the Opal Body Tone and Patterns Chart (courtesy of Opal Association – www.opal.asn.au)

Sources : 

• “Opal in South Australia”, Mines & Energy Resources, SA
• “Opal”, Qld Dept. of Mines & Energy
• “Black Opal: A comprehensive guide to cutting and orientation”, by Greg Pardey, GP Creations, 1999.
• “Opals”, by Fred Ward, Gem Book Publishers, 1997.