What are Opals?

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Opal is a hydrated amorphous form of silica, which can be found in many areas around the world.This is a dry and technical description of the most beautiful of all gemstones, which is unique, and a natural work of art in its own right. It is considered the birthstone for people born in October or under the signs of Scorpio and Libra. Opal was known to the Ancient Greek/Roman and Inca Empires, and the name opal is thought to be derived from the Sanskrit “Upala”, meaning “precious stone” or the later Greek derivative “Opallios,” meaning “to see a change of colour.”

Opal is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock.  Usually this is in the form of a thin seam or layer or within a nodule formed in a small pocket of hard white clay, commonly referred to as a “nobby”. Opal is most commonly associated with Australia, which produces 97% of the world’s supply.

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Opal Types/Terms

To help you understand a little more about opals, these are the most common terms you will come across when seeing them described :

Natural Opal – this is the generally accepted term for an opal gemstone which has been cut and polished from its rough state, without being altered or enhanced artificially.

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Black Opal – this is a term usually associated with the Lightning Ridge mines of Australia, where opal layers can form naturally over a dark black rock.  These are the most expensive and sought after opals and can cost many thousands of US dollars per carat.  However, this area can also produce opal layers over a variety of grey and white rock, and these are sometimes still referred to as “black opals”, because of the area where they were mined.  Strictly speaking they should more accurately be described as a dark or light opal, depending on the colour of the underlying rock.

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Crystal or Jelly Opal – this is where the silica layer of opal is not attached to an underlying rock at all and can be seen through.  Although generally a clear crystal, they can have various colour tints, such as chocolate, black or green etc.   The way the colour appears in these stones, as if from nowhere, is quite magical and they should not be under-rated as a gemstone.

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Fairy Opal – this is a name which seems to be mainly associated with opals from the Andamooka mines of Australia.  Here the opal has formed in tiny “pin head” flashes within a grey stone.  To enhance the colour plays, these stones are often boiled in sugar to stain the background colour to a dark brown.

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Opal Doublet – this is an opal where a very thin layer of crystal opal has been glued to a dark backing to enhance its colour plays.  This can be black plastic/brown ironstone, or any other type of stone and can be difficult to identify.  These opals can be colourful, but are not as expensive as natural opal and, in my opinion, should not be considered as an investment.  Problems can often occur, if water gets between these layers.
Opal Triplet
– this is basically and opal doublet with the addition of a further layer of domed crystal or plastic on top of the stone, which magnifies and enhances the colour still further.

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Rare opal types – are composed of silica spheres, which produce a variable display of internal colours, caused by the interference and diffraction of light passing through them.  As the composition of these spheres is random, most opals will have a completely unique pattern of varying colours.  However, some colours do occur more often than others, with red being the rarest and a blue/purple the most common. The value of a rare opal will depend upon the brightness and variety of its colours and in some cases, the rarity of its design.  One of the most sought after being “Chinese Writing”, which, as the name suggests, resembles Chinese script.

Other Terms

You will come across other terms like “harlequin”, “rainbow”, “flag stone”, “broad flash”, “rolling flash”, “herring bone”, “pin-fire flash”, “fiery opal” etc.  These are all terms used in the trade to try to best describe how that particular opal looks and to convey its individual qualities in words.


Synthetic or Artificial Opal
Sadly, like diamonds, technology has enabled opals to be made artificially on a commercial scale. The discovery of the sphere structure of precious opal led to its synthesis by Pierre Gilson in 1974. These can be difficult to detect, particularly if not familiar with opals in general.  As a guide, a natural opal will not flash a solid colour, there will be subtle undertones and slight variation in the shades of colour displayed. They can also be distinguished from a natural opal by its regularity of pattern under magnification. The patches of colour are seen to be arranged as regular “lizard skin” or “chicken wire” patterns and synthetic opals do not fluoresce under UV light.

In the Middle Ages, opal was considered a stone that could provide great luck, because it was believed to possess all the virtues of each gemstone, whose colours were represented in the spectrum of that opal.
Following the publication of Sir Walter Scott’s Anne of Geierstein in April 1829, opal acquired a less auspicious reputation. In Scott’s novel, the Baroness of Arnheim wears an opal talisman with supernatural powers. When a drop of holy water falls on the talisman, the opal turns into a colourless stone and the Baroness dies soon thereafter.
Due to the popularity of Scott’s novel, people began to associate opals with bad luck and death. Within a year of the publishing of Scott’s novel, the sale of opals in Europe dropped by 50%, and remained low for the next twenty years or so.
So the “bad luck” tag is all a lot of nonsense, generated by a popular novelist of the 19th Century.

I have described the types of opals geographically on other pages within this web site. Do not be put off buying any type of opal because of this or any of my other comments. All have a place in this industry and I hope that my brief summary has been helpful in making your choice. Natural opals are the most beautiful of all gemstones and, in my opinion, a sound investment.

Like all other natural assets, nature is not going to be producing any more in the foreseeable future and they are getting harder to find and more expensive to extract with every passing year. Always buy from a reputable dealer, ask questions and above all enjoy them…but be warned they can become very addictive!

All orders have been suspended due to the coronavirus until further notice. Thanks for your patience. Dismiss