Australian Opal: Gemstone Information
Opal is the national gemstone of Australia. Australian opal has often been cited as accounting for 95-97% of the world’s supply of precious opal, with the state of South Australia accounting for 80% of the world’s supply. Recent data suggests that the world supply of precious opal may have changed.
Australia and especially the states of New South Wales, Queensland and South Australia produce, unquestionably, the finest black and white opal. The recent books of Len Cram, illustrated with superb colour photographs, are intended, on completion, to serve as a history of opal throughout the world. Cram has illustrated and discussed the opal mines of Lightning Ridge, New South Wales, and locations in Queensland and elsewhere in Beautiful Opals.
Here the opals most commonly show a light background to the play of colour. A variety, contra luz, which shows its play of colour by transmitted light is also found. The first opal was found there in 1915 and the area is still producing fine specimens. It is the largest opal field in the world. The Andamooka field is also in South Australia; it lies nearly 600 m north of Adelaide and is particularly celebrated for crystal opal, a name given to a variety in which the play of colour appears to be set inside a transparent or translucent medium.
Opal ‘s hardness according to the Mohs Hardness Scale is 5.5-6.5 out of 10, so it should be cared for when wearing and designing jewellery with it. Multicolour Opal is sought after and can be extremely valuable depending on the specimen in question. The value of these stones is based on their properties of colour, cut, and size. A beautiful Multicolour Opal can range from Opaque to Translucent and can change in its base hue to nearly any colour imaginable. These complex combinations are what make the Opal so distinctive. Every Opal Gem can have a completely different set of characteristics and the ones that are unique, and large, are very rare and highly sought after. Queensland has for years been known as the source of boulder opal in which the play of colour is combined with brown streaks of iron-bearings and stone (ironstone).