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Types of Opal Black Opal is the most valuable Australian opal due to the small area where it is found in Lightning Ridge, New South Wales. This type of opal is easily distinguished by the blackness of the base. Black Crystal Opal is mainly mined at Lightning Ridge. These black opals show a degree of transparency and the colours are often brilliant and appear to come from within the depth of the gemstone. Boulder Opal is mined in Queensland. It is easily identified because the host rock (a brown ironstone) is left on the back of the opal. Boulder opal may be light, dark or black. It can display the same darkness and brilliance as a high quality black opal and it tends to be more freeform in its shape. The bulk of Light Opal material is found in the South Australian fields of Mintabie, Coober Pedy and Andamooka. This opal has a light body tone and is our more commonly exported opal. The brilliance, pattern, colours, shape and mark all come into determing the value of an opal Opal production has decreased over the last decade while demand has risen. Opal is like other resources we are exhausting the existing known supplies and hoping new strike will be found. The mining of opal is done by individuals or syndicate – no large companies are mining at any of the fields. Stockpiling of the gem cannot occur which means that prices are a true reflection of market demand. 
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