Opal Education: Facts, Classifications & Quality Evaluation

Opals found their way into the world in Australia’s Great Victoria Desert when a 14-year-old boy stumbled upon a patch of ground filled with inspiring stones just waiting to be plucked from the earth.

Jim Hutchinson left his son in charge of the camp while he and others went on the search for water. Little did he know that upon his return, young Willie had not only found a water source himself but a sack full of opals!😚

Opals are possibly one of the most enigmatic and alluring stones available in the marketplace whilst also being the most misunderstood.

With such huge variety, distinguishing one from another and really understanding what it is we’re even looking at can be…confusing!

In this guide, we are going to cover the ins and outs of opal education and find some clarity surrounding these charismatic stones.✊🏻

An Opal Ring With Play-of-Color Effect

Basics: What is opal?

For this in-depth guide, we must begin at the beginning, looking at the very basics of what an opal stone actually is.

Geologically, precious opals are actually rare to find and so, scientists have had a hard task understanding how this material has developed.

So, let’s clear a few things up!

Origin and history of opals

An alluring precious opal may well flash every color of the rainbow with intensity and color that is far more radiant than the fire exhibited by a diamond.

Australia became a hot spot for precious opals during the late 1800s. To be sure, Australia is considered the global leader for opal production following numerous discoveries in the early 1900s.

For over a century, their opal production went unchallenged.

Among the most famous opal mining areas are Coober Pedy, Lightning Ridge, Mintabie, Jundah, Quilpie, and many more.

But Australia is not the only place around the world that we can locate these unique gemstones.

Mexico also began opal production in the late 1800s, becoming most popular for its fire opal exhibiting bright yellow, orange, and intense red colors.

Fancy varieties of common opal can be found across the globe in areas such as Hungary, Indonesia, Guatemala, Nicaragua, Slovenia, Peru, Brazil, and several locations in the USA such as California, Arizona, and Louisiana…to name a few!

Physical Properties

Let’s get down and dirty with science!

Mineralogically speaking, opal is a hydrous silicon dioxide with a chemical composition of SiO2.nH2O. Unlike many other gemstones, the opal is amorphous which means it is without a crystalline structure.

Rather than a neatly structured interlocking collection of toy bricks, imagine the structure of opal instead as more like balls within a confined space.

The chemical composition of opal is indefinite as it contains a variable amount of water (represented by the “n” in its chemical composition).

Because of this, the opal is actually considered a mineraloid as opposed to a mineral.

How opals form

All gemstones need a juicy cocktail of ingredients mixed together under specific conditions to form.

Opal is no different.

To begin with, water filters into the earth and dissolves sand known as quartz. In turn, this becomes a silicic acid solution.

What happens next? That’s debatable!

There are several theories about how the opal then comes to be but we’ll stick to the most widely accepted theory…

Groundwater that sits near the surface evaporates as the season’s change which allows a thin layer of opal to form in the pores and seams within the rock. Opal develops within these near-surface spaces over time, creating the seams and nodules (or nobbies) that our miners dig today.

What’s the symbolism of opals?

The meaning of the opal extends into the rich history of the stone and ancient cultures.

Praised as a byproduct of lightning, deemed the physical embodiment of the rainbow, and thought of as tears to be shed over lost lovers and unnecessary wars—the opal is rich in storytelling, symbolism, and meaning.

For centuries, opal symbolism and lore associated the stone with royalty and good luck.😃 Often praised for its healing properties, it would be held up to the eye to cure eye diseases.

Many spiritual leaders and healers consider opal to help regulate insulin in the body, help during childbirth and PMS as well as detoxing the liver.

A passionate stone associated with lust, desire, seduction, and love the opal also found some negative superstitions along the way.

It used to be believed that opal could render the carrier invisible when wrapped in a fresh bay leaf. This superstition earned opal the title of Patronus Furum, Latin for the patron of thieves.

Understand the 6 types of opal classification

Opal can be a somewhat confusing stone when it comes to the buying process as there is such a wide variety to choose from!

To break it down, we’re going to look at the 6 types of opal classification that you can consider when it comes to choosing the perfect opal for you.

These make it easier to distinguish between what’s what!

Common Opal vs. Precious Opal

Precious Opal

A precious opal exhibits extraordinary flashes of iridescent color when moved in space, viewed from different angles or when the light source is moved.

In the industry, this term is called "play-of-color".🌈

And this play-of-color is what makes the opal such an exquisite and sought-after gem. Precious opal can flash all colors of the rainbow including red, purpose, bright yellow, orange, green or blue.

And, when seeking a precious opal, its attraction usually lays in its color intensity, diversity, uniformity, pattern, and capability to be seen from any angle.

Australia still holds the crown for most precious opal mined to date.

And precious opals are RARE! They can only be found in very limited locations around the world including Ethiopia, Mexico, Brazil, USA, Honduras, Indonesia, New Zealand, Poland, Guatemala, Canada, Zamia, and Peru.

An Oval Precious Opal Gem

Common Opal

Unlike the precious opal, common opals do not possess this play-of-color. Although far less glamorous, the common opal has been given its name from the fact that, well, they’re pretty common!

They can be found in many locations around the world and as well as this, their appearance may well also be considered "common". These opals do not generally attract commercial attention.

This is not to say that the common opal isn’t also a beautiful gemstone.

Once cut and polished they can be incredibly attractive and still have a high appeal which is why they can still be cut and demand a reasonable price as a gemstone.

ADDED BONUS!
To add something else into the mix, we can also consider the Fire Opal which is not to be confused with precious or common opal.

The fire opal may or may not display any play-of-color. It is a term used for both colorful transparent and translucent opals that have a fire-like background color of yellow, orange, or red.

Despite the term "fire opal" which might make us assume that the stone is precious, play-of-color is not always present in fire opal.

Natural Opal vs. Assembled Opal

Natural opal is the name given to opals that have been naturally mined from the earth. With the opal gaining popularity, many have been able to replicate its appearance but, with a little knowledge, it is easy to spot the real deal!

Assembled opals are made from opal rough that has a thin but gorgeous layer that has a wonderful play of color that would truly be a shame to waste.

Because of this, we have opal doublet and opal triplets.

  1. Opal doublets are two-part stones where a thinly cut layer of opal is placed on a base of either obsidian, potch, basalt or plastic.
  2. Opal triplets take this one step further and glue a transparent dome of quartz or plastic on top of the opal for added protection and durability against any possible damage.

Solid Opal vs. Boulder Opal vs. Matrix opal

Solid Opal

The solid opal is what most of us think of when we think about a classic opal. This type of opal is also known as Type Ⅰ Opal and can be a combination of both common and precious opals.

This particular term is used for a rough-cut opal stone that only consists of opal material. So there isn’t any presence of host rock or significant inclusions within the stone.🧚🏻‍♂️

Boulder Opal

Now, the boulder opal is considered a Type Ⅱ Opal and is the term coined for a rough or cut opal that displays precious opal within or attached to, its host rock.

The specimens of these boulder opals are a great way of unveiling the opals’ origin. With many boulder opals occurring in thin seams and layers they can be carved into a stone that only displays the precious opal in the face-up position.

To be sure, there can be a stark contrast of color in a boulder opal!

The bold flashes of color present in the precious opal are enhanced by the dark hue of brown sandstone or backing of black basalt.

The natural appearance of the boulder opal is incredibly alluring to many opal lovers as it provides a level of education, uniqueness, and beauty.

Matric Opal

The matrix opal, also known as Type Ⅲ Opal, may appear similar to the boulder opal but in reality, they are quite different.

In a boulder opal the host rock forms within the seams and fractures of the opal yet with matrix opal, the precious opal is intimately mixed with its parent rock.

Matrix opal is often most found in sedimentary rocks such as limestone, sandstone, chert, or ironstone with some found in igneous rocks such as basalt, andesite, or rhyolite.

Andamooka in Australia is the world’s most famous region for these matrix opals!

Classified by the base color

White Opal or Light Opal

These opals are named according to their white, yellow, or cream body color.

This particular white opal was generally what came to mind in the United States when most people thought about the word "opal" because other varieties rarely graced the jewelry store windows in the United States over the last few decades.

Of all of the precious opals, the white or light opal is the most common.

Black Opal or Dark Opal

As you may have guessed, the black or dark opal is the term used for opals of dark body color such as black or dark grey. It also encompasses opals that are dark blue or dark green in body color.

Within these stones, the play-of-color is often more obvious and makes a glorious display of movement and depth within the stone which makes them incredibly desirable!🤳🏻

These particular stones can be sold for very high prices with the right body color and face-up play of color.

Yellow Gold Halo Style Blue Opal Ring

Blue Opal

Blue opal is a beautiful material that lends itself perfectly to the creation of beads and cabochons (a gem that has been polished but not faceted).

A highly regarded variety of common opal, the blue opal is mostly sourced from Oregon, Peru, and Indonesia. Each area offers a blue opal with its own unique character specific to its place of origin.

  • Oregon brags of the Owyhee blue opal which can range from light to dark pastel blue.
  • Peru offers blue opal beads that can sometimes contain tiny translucent areas that exhibit play-of-color.
  • And the blue opal found in Indonesia is most often associated with opalized wood.

Crystal Opal

Crystal opal is a truly magical and opulent opal that is named according to its translucency or semi-translucency that flashes surprising play-of-color form within the stone.

To be sure, the crystal opal is a challenge for any jewelry designer as they must create a setting that allows light to enter and exit the stone from lots of different angles in order to take full advantage of its play-of-color!

More recently, Ethiopia has been a great source of crystal opals but Australia was the first abundant source of crystal opal.

Pink Opal

Yes, the variety of colors is endless! We can even find opals in a variety of shades of pink! The most common of these pink opals are mined in Peru with a small amount of pink opal found in Oregon and Mexico.

The pink opal is a type of common opal and ranges in color from almost white to a near lilac color.

Morado Opal

Any linguists here?

Morado is the Spanish word for "purple". There are not many sources in the world that produce a rich purple opal but these common opals with a purple body color can be found in parts of Mexico.

Other opals classified by the base color
As we can see, there are a huge variety of base colors available to us! And there are many more than the ones mentioned above including brown crystal, semi-black, gray, orange, semi-crystal, jelly opal, boulder black, and boulder brown.

Classified by pattern

Harlequin Opal

Within a Harlequin opal, we will find areas of color in the chape of either diamonds or rectangles which is what makes this particular opal quite distinguishable.

This Harlequin color pattern is most often present on the face of the stone in a two-dimensional display. However, we can sometimes see these patterns in a three-dimensional display within a more transparent stone. (Although this is rare!)

Contra-Luz Opal

The contra-luz opal is a particularly intriguing opal as we can only see any play-of-color within this stone when the light source is directly behind the stone.💡

Without this, the stone appears transparent or semi-transparent.

Because of this, the contra-luz opal can also be a challenge for jewelry designers who must be able to set the opal in such a way that allows light to pass through.

Cat’s-Eye Opal

The cat’s-eye effect that is present across the surface of a cats eye opal is also known as chatoyancy.

Although a rarity, opals with the cat’s eye effect exhibit a thin line of bright white light that is reflected from a parallel network of needle-shaped inclusions from within the gem.

As the stone is moved or the light source is moved, the line (or "eye") moves along the surface of the stone.

Pinfire Opal

The pinfire opal has a very distinguishable appearance, portraying pinpoints of color throughout the stone. There are clear, neatly defined specks throughout the stone that contrast against its body.

Other opal varieties classified by pattern

  • Chinese Writing - Has the appearance of Asian scripture
  • Floral - A variety of repeated, larger patterns similar to that of a floral dress pattern
  • Palette - Resembles the patterns that form on an artists paint pallet
  • Peacock - Predominantly blue and green play-of-color resembling a peacock’s feather
  • Flame - Offers streaks of red fire moving across the surface of the stone
  • Flagstone - Similar to Harlequin and features large, close sitting patches of color. Very rare!

Classified by geography

  • Australian Opal - For over 150 years, Australia has been a leading source of opal production.🦘 A wide variety of opal can be found across the country including precious, black, matrix, boulder, jelly, and common.
  • Andamooka opal - One of the early mining areas in South Australia. Famous for its matrix opal, commercial production began here during the 1920s.
  • Coober Pedy Opal - Coober Pedy is a little town in Australia that settled in 1916 when the first opal mining production began. It was handsomely nicknamed Opal Capital of the World as it became prolific in the opal mining industry. Famous for producing white base color opals, its production has been uninterrupted since it first began.
  • Lightning Ridge Opal - Lightning Ridge is a town in New South Wales, Australia, world-famous for its deposits of black opal. More black opal has been produced here than in any other place on earth.
  • Ethiopian Opal - Precious opal, fire opal, and beautiful common opals are often found in Ethiopia. Ethiopia took its place in the market in 1994 and has since taken a considerable amount of market share away from Australia!
  • Honduras Black opal - Most opal lovers will know exactly what you’re talking about when you say "Honduras black opal". Honduras is best known for its black, basalt matrix opal with its tiny spatterings of play-of-color.
  • Mexican opal - Mexico is perhaps our most important source of fire opals. They have a bright yellow, orange, or red hue that is cut into stunning cabochons.
  • Louisiana Opal - Louisiana opal is a quartzite cemented with precious opal mined in Vernon, Louisiana. Within these stones, you can quite clearly see the grains of quartz filled in between with a matrix of clear cement that produces an opulent play of color under the correct light.

Things to consider when evaluating the quality of an opal

When evaluating the quality of an opal we need to look at a mixture of the 4Cs framework along with specific characteristics and specifications that are relevant only to the sumptuous opal.⚠️

There are many opal quality factors to take into account so, let’s begin!

Color

When it comes to evaluating the value of an opal, color takes precedent. So, when considering the color of any opal we are wanting to take into account the number of colors present, the clarity of said colors, the brightness of fire play, and play of color coverage.

Clarity of Colors

The clarity of an opal’s color is distinguished in terms of hue, tone, and saturation. For the most part, opals with greater depth of tone and saturation are considered of higher value.

A bright and pure blue would be considered more valuable than a paler, greyish blue. And whilst a pink opal may be desirable, it is less so than a pure red opal.

Brightness of Fire

The brightness of an opal’s fire or play of colors can be graded on a scale of 1-5.

GradeDescription
1 - FaintLittle play of color under direct light and none under low light
2 - DullSome color under low light, but seemingly dull even under indirect sunlight
3 - BrightFair color under low light but with nice fire under indirect sunlight
4 - Very BrightGood color under low light with sharp and impressive color under indirect sunlight
5 - BrilliantExceptional color under all lighting conditions.

Color Coverage

For a highly prized opal, we need to assess the coverage of the opal’s unique coloration. When we’re talking about the coverage we’re really talking about the amount of surface area that exhibits play-of-color.🔍

In an ideal world, the entire crown of the opal should show fire that is evenly distributed.

When an opals play-of-color is off-center, they become less valuable. So what we are looking for here is an evenness in play-of-color distribution!

Patterns

Already we have covered patterns such as the Harlequin and pinpoint patterns that can be seen within certain opals.

But it is worth noting that there are a wide variety of shapes and patterns that we can find among the vast world of opals. These might also include a windmill, peacock, and flame.

It is generally considered more desirable to have an opal with larger, more closely gathered patches of color as opposed to smaller, scattered dots of pattern.

However, this still comes down to personal preference and both are irrelevant if the opal does not display a bright and engaging play-of-color.

Comparing Between Different Patterns of Opals

Directionality

Directionality is very specific to the opal and one of the most important factors in determining the quality of the stone.

What we want in a glorious opal is for its play-of-color to be seen from as many possible angles as possible. If we have to turn and adjust the stone to find its flashes of light and patterns within the stone then the opal is likely not optimized for exceptional play of color.🤓

Clarity & transparancy

Where opals are concerned its clarity is evaluated by its degree of transparency and lack of inclusions. In this case, an opals clarity can range from opaque to completely transparent.

This is where things become a little tricky!

Because experts will appreciate different levels of clarity for different opals.

For example, a crystal opal may perform better when it is more transparent whereas a black opal would be preferable with an opaque background.

Like all gems, opals can incur fractures, inclusions, and other surface blemishes and in most cases, the fewer the better! However, this again can be difficult to determine when we have matrix and boulder opals (for example) that have been so named precisely because they have elements of host rock within the opal.

Inclusions in opals can include non-opal spots, sand, chips, webbing or sandstone between the areas of color, and fractures.

The presence of these will affect the value of the opal depending on how it affects the appearance of the stone.

Cut

Unlike most other stones, color is the most important aspect of the opal when deciphering its value. However, the cut will always have its part to play.

Ultimately, the job of the opal cutter is to enhance the natural color of the opal.

Exceptional opals are not to be cut to a standard size or shape but cut into irregular shapes that optimize for spectacular play of color and save as much of the opal rough as possible.😎

Irregular shapes in the opal world are highly prized for their uniqueness and characteristics however, commercial quality white opal, assembled opal, and cabochons are often set to calibrated sizes and shapes, with an even and symmetrical finish.

Carat

Even carat weight does not have a huge amount of relevance in the valuation of an opal. Typically, larger opals do not demand as high a price as mid-sized stones with the most expensive gems sitting between five and ten carats.

With its lower density, even larger opal stones can be comfortable to wear in jewelry.

Character

It’s incredibly important to note that the purchasing of an opal should be very much down to personal preference.

As you’ve seen, there is so much variety, so much choice available that while we can follow certain guidelines to ensure we have what the industry would consider a "high-quality opal" it is very much an emotional decision.🤴🏻

When purchasing your opal, you must consider what you find attractive, desirable, and a great representation of your own personality.

There is so much character to be found in these stones that they cannot easily be put into a box of "one size fits all".

How to care for opal stones?

So, you’re thinking you’d quite like an opal? Let’s go over how you can care for this relatively soft stone:

  • Opals sit at a 5.5 to 6 on the Mohs scale of hardness and so are a relatively soft stone in comparison to others. Durable enough to be worn within our jewelry but susceptible to damage if not properly taken care of. This is why we recommend always removing your opal jewelry before any physical or outdoor activity.
  • Solid opals cannot be damaged by water but suffer in very dry temperatures or rapid temperature changes. We advise keeping any solid opals in a plastic bag alongside a damp cloth to keep them hydrated.
  • Doublets or triplets should not be soaked in water for too long as the back may come away or even fog up the top layer of the stone.
  • The opal is fairly soft and fragile compared to other stones! Make sure to store them separately from other jewelry wherever possible.
  • Gently clean with warm water and a soft toothbrush. Avoid any harsh chemicals or cleaners and never place your opals in an ultrasonic cleaner if you want them to last!

Fun read: The famous opals in the world

Let’s end this article on a fun note, shall we?!

Here are a list of just some of the most incredible opals from around the world, and boy, are they stunning!🍭

The Aurora Australis

The Aurora Australis exhibits an impressive harlequin pattern in blue, green, and red. This opal weighs in at 180 carats and is valued at an estimated AUS $1,000,000! It was discovered by Charlie Dunstan in Lightning Ridge in 1938.

The Fire Queen

Also known as the ‘living ball of fire’, the Fire Queen is another of Charlie Dunstan’s discoveries. This 900-carat behemoth was added to  J.D. Rockerfellers collection in 1949 for £75,000.

The Empress of Australia

Considered one of the finest black opals ever to be mined, The Empress weighs in at 500 carats! Its exquisite array of color meant that it was originally named ‘Kaleidoscope Queen’

The Butterfly Stone

Founded in World War I, this unique opal isn’t as big as others with its 51 carats but, its unique shape is said to appear like a Spanish dancer in a ruffled dress when placed on its side.

The Virgin Rainbow

The most recent of these celebrated opals is the Virgin Rainbow mined in Coober Pedy. This luminous opal really does exude every color of the rainbow and weighs in at 72.65 carats and is over 6cm in length.

Everything you could need to know about opals!

Phew! We made it!🐝

There is certainly a lot of information to consider where these enigmatic beauties are concerned but just remember, when it comes to buying opal stones (either individually or as a jewelry piece) we can certainly follow quality guidelines but it will very much come down to personal preference.

The unique character, mystical nature, and sheer variety available make it impossible to follow strict rules when it comes to buying an opal.

Trust your gut instinct and find a stone that is aligned with who you are and what you desire.

The rest is history!

Thinking of opal for your next ring purchase? Check out our opal ring buying guide!

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