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Opal is a non-crystalline mineral formed from the combination of silicon dioxide (SiO2), water (H2O) and heat induced pressure.
95% of Opal is sourced from Australia.
The name ‘Opal’ originates from the Greek Opallios and the Latin Opalus which both mean to “see a colour change”.
The Opal is one of the seven most recognised gemstones in the world. It is also the October birthstone. It represents love, happiness and hope.
It will take approximately 6 million years for a centimetre of Opal to form. The Opal could be said to be a miracle created by nature and the land of Australia.
Name Opal
Formula SiO2·nH2O
Crystal Habit Non crystalline mineral, Irregular veins
Specific Gravity 2.1
Mohs Scale 5-6.5
Attribute Sedimentary Opal−Australia Opal Volcanic Opal–Hydrophen Opal-Mexico and Ethiopia (There are exception)
Origin Australia Mexico and 8 or more Country (95% of Gem Opal are from Australia)

Type of Opal

Black Opal​

The Black Opal is the most valuable and rarest opal. The general body tone can range from grey to a jet black. The iron oxide and carbon trace elements create the dark tones, and the bright colours of the opal contrast the body tone to appear more vibrant. The majority of the world’s Black Opals are being mined from Lightning Ridge in New South Wales, Australia.

White Opal

The White Opal is a more common type of opal. It has light body tones ranging from white to a cream-colour. While the vibrancy of the colours are not as obvious as they are with the black opals, the colours are still beautiful. These opals are mined in South Australia in places such as Coober Peddy, Andamooka and Mintabie.

Boulder Opal

The Boulder Opal is the second most valuable type of opal. They are mined from large ironstone boulders under the ground. Thin vessels of opal appear in the cracks and fissures of the boulders. Boulder Opals often have a dark body tone (similar to the Black Opal) which makes the colours of the opal appear more vibrant.

Body Colour

O.G.S. adopts a scale of darkness through to lightness to classify the body colour of opal. The scale consists of five (5) classifications of dark body colours ranging from B1 through to B5 and two (2) classifications of light body colour L1 and L2.

Colour Play

Opals can be categorised according to the diffracted colours displayed in the face of the stone. The spectrum of colours ranges from red which is the rarest of all the colours, through to orange, gold, green and blue violet. Under O.G.S., when a stone displays up to three (3) colours, the most prominent colour is then noted followed by the term “multi”. e.g. an opal showing red, blue, green but red being the prominent colour – we can say that “opal as multi coloured with red. The brightness and intensity of the colour in each opal will be directly affected by the body colour in which the colour play occurs

Colour Pattern

This is the classification of the pattern formed by the various colours. Those patterns are largely classified into 8 types.
  • Harlequin
  • Rolling Flash
  • Pin Fire
  • Floral
  • Broad
  • Ribbon
  • Galaxy
  • Straw

Cut and Cabochon

  • The ‘cut’ refers to the shape of the stone when viewed from above.
  • The ‘cabochon’ refers to the height of the dome when viewed from the horizonal.

Glossary of Opal Terms

Andamooka A town in Far North South Australia, where White Opals are mined.
Artificial Opal Man-made Opals that have a similar appearance as a natural Opal.
Bezel Setting A type of setting which holds a gemstone in place using a vertical rim.
Black Opal A type of Opal found in Lightning Ridge, New South Wales. It contains a dark body colour.
Boulder Opal Opals found in ironstones of Queensland. These Opals are cut with the ironstone.
Broad A type of Opal colour pattern. Please see our Colour Pattern Chart for more details.
Cabachon A type of cut whereby the Opal is cut from the top to create a dome.
Cachoron Quartz
Cameo Material that is carved with a raised relief.
Carat A type of unit used to measure the weight of Opal.
Clarity The transparency and the amount of inclusion in the Opal.
Clasp A device used to interlock and fasten parts together; for example on a necklace.
Claw Clasp A type of clasp which can be pushed to open and released to close.
Colour Pattern The pattern of colours that can be seen on Opals. Please refer to our Colour Pattern Chart for more details.
Common Opal Opal that has no value or gemstone quality.
Coober Pedy A town in northern South Australia, also known as the ‘Opal Capital of the World’. White Opals are commonly mined from this town.
Crazing Lines that are sometimes made in the process of the evaporation of the moisture in Opals. Crazing may look like multiple crack lines.
Cut The process of cutting and polish a rough Opal stone.
Cutter Opal cutting specialist.
Dead Spot A spot on an Opal which may show no colour or may appear different.
Dome A shape which is round and curved on one side.
Doublet A type of Opal which uses an artificial backing to enhance the colour and pattern of the Opal.
Dumortierite A type of quartz which contains coloured aluminium boro-scilicate mineral.
Enhancement The process of increasing or improving the quality or look of the Opal.
Eromanga An area in Outback Queensland which is named after the Aboriginal word meaning ‘hot, windy plain’. Opals are found in the Eromanga area.
Fire Opal A type of Mexican Opal which is transparent red in colour. It is made in volcanoes.
Floral A type of Opal colour pattern. Please see our Colour Pattern Chart for more details.
Free Shape A type of free cut without a defined or particular “shape”.
Galaxy A type of Opal colour pattern. Please see our Colour Pattern Chart for more details.
Ground Colour The colour of the bottom of the Opal.
Harlequin A type of Opal colour pattern. Please see our Colour Pattern Chart for more details.
Heated Opal A type of Opal that is “heated” with sugar and sulfuric acid to create a look similar to Black Opals.
Hyalite A type of Opal made in a volcanic eruption.
Hydrophane A type of Opal made in a volcanic eruption.
Inclusion Material that can be found in Opal, suc as air bubbles and vegetation matter.
Intaglio A type of carving that is the opposite of Cameo.
Lightning Ridge A town in New South Wales where Black Opal is commonly mined.
Matrix A type of Boulder Opal which contains the Opal intertwined in the ironstone.
Mintabie An Opal mining community in the Anangu Pitjantjatjara Yankunytjatjara lands in South Australia.
Moss Opal Opal that contains iron and manganese.
Nobby Stones that contain Opal inside.
Non-crystalline Mineral Mineral which does not contain crystals or a crystalline structure. Opals are examples of this.
Opalos The Latin word for “Opal”.
Opalios The Greek word for “Opal”.
Opalton One of the largest Opal fields in Queensland, known for Boulder Opals. Also known as Opaton Fields.
Pin Fire A type of pattern of colours that can be seen on Opals. Please refer to our Colour Pattern Chart for more details.
Play of Colour Effect The different colours that can be seen when the Opals are viewed from different angles and under different lights.
Potch A part of the Opal that may not show colour. Colours may range from grey to black .
Precious Opal High gem quality Opals; opposite of a Common Opal.
Quartz A crystalline mineral made of silicon and oxygen.
Quilpie A location in Queensland where Boulder Opals are often found.
Ribbon A type of pattern of colours that can be seen on Opals. Please refer to our Colour Pattern Chart for more details.
Rolling Flash A type of pattern of colours that can be seen on Opals. Please refer to our Colour Pattern Chart for more details.
Rough Unpolished and uncut Opal.
Rub Opal that has polished and unpolished sections.
Sedimentary Opal Opal that is formed in the earth as water flows through the earth, picking up silica from the sandstone. These Opals can be found in sedimentary rocks.
Silica, Silica Gel Mineral that Opal is made of.
Silicon Dioxide A natural compound made of silicon and oxyden. Also known as silica.
Treatment The process of changing colours on Opals using artificual processes.
Triplet A type of enhanced Opal which contains a backing to enhance the colour, a thin slice of Opal and a clear layer to mimick a natural Opal.
White Opal A type of Opal which contains a light or ‘milky’ body colour.
Window A transparent part of the Opal.
Winton A location in Central Western Queensland which Boulder Opals are found at.
Wood Opal Opal found in fossilised wood and crystallised.

Opal Chart

This panel is used by our customers in the store to explain the Opal System Chart.


There are three types of natural opals. Namely black, boulder and white opals. There are also imitation opals which are called the triplet and doublet opals. Please come to study more.


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