What Are Opals

Friday, 30 September 2022
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Opal colours and patterns

What Is an Opal?

What are Opals? The word Opal is derived from Latin and literally means “to see a change in colour”. A perfect description for Australia’s national gemstone.

Opals are regarded as one of the traditional gems however they have grown to become one of the most popular gemstones in the world. One reason for this popularity maybe because there is an opal for every budget and so everyone can own one. This does not mean that opals are cheap, as the highest quality opals can be more expensive per carat than diamonds or other traditional gemstones.

What are the three opal varieties?

Opals are chemically silicon dioxide and water, with the amount of water varying in each opal, they are therefore classified as a mineraloid. The three main types of opal are “Fire Opals”, “Boulder Opals” and Common Opals”.

So what actually is an Opal?

The chemical definition is a hydrated variety of amorphous silica. That is opals are a form of silica, the most common of which is quartz. Opals contain water which distinguishes them from quartz but means that they are less hard and more brittle.

Some opals demonstrate a phenomenon known as “Play of Colour”. This is caused when the internal structure of the opal consists of regularly packed spheres which have the effect of diffracting the light into its component colours like a prism. An opal with such qualities is considered to be a gemstone.

What colours do opals come in?

Opals come in a huge variety of colours. The basis of the colour is the bodycolour of the opal. The most common bodycolours are white, grey, black or brown, but it can be any colour. The most popular and beautiful are green, blue, red, orange or yellow.

The physical properties of Opals

Opals have small spheres of silica which are generally arranged into a regular pattern. There is water in between the spheres which causes it to be brittle in some instances. When light is diffracted by the spheres this is called opalescence.

Transparency and Translucency, also known as Pellucidity are characteristics of opals and relate to the physical properties which allow light to pass through the opal. The various categories are translucent, opaque and semi-transparent. Occasionally an opal shows a transparent quality.

Opals have the same base chemical formula as Quartz but the inclusion of water in the gemstone means its physical properties vary greatly.

Are opals rare?

Opal is found throughout the world and is a very common resource. The majority of opals, over 90%, are found I Australia, where is the national gemstone. The majority of opals existing are Common Opals which lack the “Play of Colour” found in other rarer and more valuable opals.

Opals which display “Play of Colour” are rare and rarer in the size that can be cut to produce valuable gemstones. Play of Colour is able to be viewed in 3 situations, firstly when the stone is moved, secondly when the angle the stone is being viewed from is changed, and thirdly when the light source is changed.

Can opals be fragile?

Yes. Opals make magnificent gemstones for jewellery which can be considered low contact, such as earrings, brooches and pendants. Due to its chemical makeup opals are more easily chipped than other gemstones. So it is wish if the opal is to be used in a ring a bezel around the opal will greatly protect the stone from chipping caused by contact with harder surfaces. It may also be wise to remove during actitites will may be considered dangerous. (Link to jewellery protection post)

Sources of Opal

Since the end of the 19th Century Australia has been the most important source of opals with over 90% of all opals mined sourced from Australia. Opals occur in various regions and the place where they are mined describes the opals, such as Coober Pedy, Lightning Ridge, Mintabie, Andamooka Yowah, Koroit, Jundah, and Quilpie.

Opals are found in other parts of the world, notably Mexico, Ethiopia, Hungary, Indonesia, Brazil, Peru, Honduras, Guatemala, Nicaragua, Slovakia, USA and the Czech Republic.

Types of Opals

Being such a relatively common gemstone there are numerous names to describe the various types of opals. Often there is an obvious and logical logic behind the general category with examples of, fire opal, black opal, boulder opal, Coober Pedy, Mintabie, and Andamooka being just a fraction of the names allotted to various types of opals.

Common Opals

The most abundant and least valuable of all opals. Common Opals are overlooked as they are often mistaken for quartz due to their unremarkable visual appearance. Common Opal can have colour, pattern and beauty that can be anything but common. However, common opals do not exhibit Play of Colour although some examples can be attractive and colourful and can be highly polished and can be cut and sold as a gemstone.

Precious Opals

Precious Opals are distinguished from Common Opals because they display the “Play of Colour”. Or fire within the opal. This is what makes precious opals so attractive and desirable. The play of colour is the phenomena of the gemstone to reflect all seven colours of the rainbow but necessarily all in one stone.

White Opals

White opal colours tend to be pale and delicate on a light coloured background. The Coober Pedy area of South Australia is the most famous for producing white opals. While less spectacular than other types of opals White Opals can be very beautiful and command reasonable prices.

Black Opals

Black opals are the rarest and most valuable of opals. They have a dark background with background colours ranging from red, purple, through to greens and blues. One of the things that makes Black Opals so desirable is the contrast of the “Play of Colour” to the body colour of the opal. Lightning Ridge in Queensland Australia is known as the Black Opal Capital of the World producing the vast majority of this beautiful gemstone.

Boulder Opals

Boulder Opals are different from all other types in that the opal is attached to the host rock, generally ironstone. The vein of opal can often be thin hence the “backing” of the host rock. The opals can be black or light. They are found in a large area of Western Queensland, Australia.

Matrix Opals

A Matrix opal is formed when the host rock penetrates the opal and is visible in the gemstone creating a vein line network. The most common base rock are with ironstone, sandstone, or claystone, though some have basalt.

Author Bio.

Jill Hansen runs Anastasia’s Of Broome and is a highly recognised expert in both the fields of South Sea Pearls and Diamonds. Jill trained in seeding pearls in the Cook Islands by Japanese Pearl Technicians, and established a wholesale pearl business selling pearls all over the world. She pioneered the combination of pearls and diamonds to create Lust™ Pearls, a unique fusion of these two beautiful gemstones. Jill holds the prestigious recognition of being an Antwerp Diamond Broker for selecting and sourcing Diamonds direct from the diamond capital of the world, Antwerp. She is a diamond expert and is happy to use and impart her knowledge to help customers make informed decisions.


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