Types of Opal

Opal is an amorphous mineraloid that comes in many unique varieties based on the location it was sourced from. The two main types are Precious and common Opal. When speaking of opal people are generally referring to precious opal. The majority of precious opal is mined in Australia where over 96% of the world’s supply is produced. Notable mines in Australia include Coober Pedy, Lightning Ridge, Lambina, Mintabie, Andamooka, Yowah, Koroit, Jundah, Winton and Quilpie. Other countries that produce both precious and common opal include; Brazil, Czech Republic, Ethiopia, Guatemala, Honduras, Hungary, Indonesia, Mexico, Nicaragua, Peru, Slovakia and the U.S.A.

Types of Opal

Opal is an amorphous mineraloid that comes in many unique varieties based on the location it was sourced from. The two main types are Precious and common Opal. When speaking of opal people are generally referring to precious opal. The majority of precious opal is mined in Australia where over 96% of the world’s supply is produced.

Lightning Ridge Opals

Coober Pedy Opals

Boulder Opals

Fossil Opals

Opal Jewellery

Common Opal

Common opal is found throughout the world and does not possess a “play of colour” like precious opal. Most specimens of opal are common in appearance and so they don’t attract the same attention as precious opal would. Although common opal presents no play of colour it can be vividly colourful and the stone will accept a high polish such that some forms of common opal are still highly sought after.

Common Opal

Common opal is found throughout the world and does not possess a “play of colour” like precious opal. Although common opal presents no play of colour it can be vividly colourful and the stone will accept a high polish such that some forms of common opal are still highly sought after.

Precious Opal

Precious Opal is determined by opal that presents a “play of colour” along the surface of the stone. This “play of colour” is what determines whether an opal is classified as precious or common. Flashing with iridescent colours when viewed from different angles, when the light source is moved, or the stone itself is moved. These flashes are what is known as the opals “play of colour” and can come in a multitude of colours such as indigo, purple, blue and green from lower wavelengths of light passing through the stone to yellow, orange and red from the higher wavelengths passing through. “Play of colour” is what makes opals such a popular gemstone with the higher wavelengths being of considerable value.

Precious Opal

Precious Opal is determined by opal that presents a “play of colour” along the surface of the stone. Flashing with iridescent colours when viewed from different angles, when the light source is moved or the stone itself is moved. 

How Opal is Valued

The methods used to determine the value of an opal incorporates many different attributes of the piece.

Body Tone

Body tone rating is based on the opals face up shade rated against a scale of 1-9.

Vividness

How the colours appear impacts the value of an opal greatly. With the best stones shining brilliantly in any lighting conditions.

Colour

Precious opal can display the entire visible spectrum of colours. The most common colours being blue and green, with red being the rarest.

Pattern

The pattern of opal can dramatically increase its desirability. with the harlequin pattern being the rarest.

Inclusions

The natural process that forms opal causes inclusions to appear when cutting the piece. Sand spots appear within or on parts of the opal that can affect the desirability and value of the piece.

Colourless Areas

As opal forms, some areas may not align into uniform rows correctly, and this will produce common opal alongside precious opal when cutting this common opal can sometimes be used to create stunning patterns that enhance the value of the stone.

Fractures

Fractures can appear within unstable opals and may cause the stone to break from the temperature simply changing. Luckily Australian opal is generally very stable and so is not prone to suffer from fractures.

How Opal is Valued

The methods used to determine the value of an opal incorporates many different attributes of the piece.

Body tone rating is based on the opals face up shade rated against a scale of 1-9.

How the colours appear impacts the value of an opal greatly. With the best stones shining brilliantly in any lighting conditions.

Precious opal can display the entire visible spectrum of colours. The most common colours being blue and green, with red being the rarest.

The pattern of opal can dramatically increase its desirability. with the harlequin pattern being the rarest.

The natural process that forms opal causes inclusions to appear when cutting the piece. Sand spots appear within or on parts of the opal that can affect the desirability and value of the piece.

As opal forms, some areas may not align into uniform rows correctly, and this will produce common opal alongside precious opal when cutting this common opal can sometimes be used to create stunning patterns that enhance the value of the stone.

Fractures can appear within unstable opals and may cause the stone to break from the temperature simply changing. Luckily Australian opal is generally very stable and so is not prone to suffer from fractures.

Synthetic and Treated Opal

Synthetic Opal 

Synthetic opal, also known as Opaline Silica, is produced in a laboratory attempting to mimic the natural process that forms precious opal. Generally showing bright colours in regular patterns, synthetic opal can be easily identified from naturally formed opal. Other methods of imitating opal include embedding coloured tinsel into clear resin or plastic. 

Treated Opal 

There are many ways to treat opals. However, almost every form of treatment will drastically reduce the value of the piece. Methods to treat opals include smoking them or acid bathing the pieces. 

Synthetic Opal 

Synthetic opal, also known as Opaline Silica, is produced in a laboratory attempting to mimic the natural process that forms precious opal. Generally showing bright colours in regular patterns, synthetic opal can be easily identified from naturally formed opal. Other methods of imitating opal include embedding coloured tinsel into clear resin or plastic. 

Treated Opal 

There are many ways to treat opals. However, almost every form of treatment will drastically reduce the value of the piece. Methods to treat opals include smoking them or acid bathing the pieces. 

Australian Opal Types

Precious Opal

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Boulder Opal

Boulder Opal is mainly found in Central Queensland Australia.

It is renowned for its unique patterns with notable pieces coming from Koroit and Yowah.

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Crystal Opal

Crystal opal is translucent or transparent but still shows the play of colour within the material and can appear as either dark, light or white opal depending on the trace minerals that will affect the body tone of the opal. 

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Fossil Opal

As opal forms there is a possibility that it will replace minerals in shells, bones and other organic material taking on and retaining the shape. Some spectacular examples are opal pineapples from White Cliffs, NSW and Eric the opalised Pliosaur. 

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Common Opal

Potch Opal

Potch is commonly found while mining for precious opal and comes from many regions and in many colours. Some Potch opal can be cut and polished to produce some beautiful and unique patterns, while some will present sun flashes. 

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