I suppose it was my love of colour that first attracted me to these gorgeous gems, shifting, sparkling full of fire, I love precious Opals in all their variety, no other stone holds quite the same fascination for me. From the exquisite fire (schiller) in a strand of crystal or the play-of-colour in black Opal, to the earthy exuberance of boulder Opal or totally intriguing opalised snails and shell. For me Opal has it all. So I thought I would share a little of what I have learned of these amazingly beautiful gems.
What exactly is Opal you may ask, well its chemical composition is Si0².nH²O hydros silicone dioxide and it always contains water between 3 and 30 per cent. Hardness is 5 1/2 – 6 1/2 on the Mohs’ scale. Opals rainbow hues are caused by minute spheres of the mineral cristobalite in silicone jelly which causes the diffraction of light and gorgeous patterns. None of which prepares you for how lovely it can be!
Opal’s special characteristic is the play-of-colour which changes with the angle you view it from, and the way light strikes it to make flashes of rainbow colour called schiller. Some stones can dazzle with their intensity, while others have pinpoints of colour or a gentle haze, to me all are beautiful. Some of the most amazing examples command prices per carat higher than that of diamonds! The more play-of-colour an Opal displays, the higher the price. Red appears to demand the highest prices while shades of blue or green tend not to be so costly, although I personally love the blues, greens, purples etc.
Fragile, as well as beautiful Opals are sensitive to knocks, pressure, acids and alkalis. Heat can cause the water within to evaporate, it can then crack or even lose its colour!
Therefore Opal needs careful handling it should be stored and allowed to stabilise before it is cut to produce beads, jewellery or carvings, otherwise it can crack or fracture producing a network of fine lines or “crazing”. These changes cannot be reversed, so it is always best to buy from a trusted source, with an excellent reputation when choosing your Opals.
Body colour in Opal, this is the background against which the opal fire plays. Crystal opal is clear and colourless. white opal has an opaque or milky colour , grey is like the white but with a grey overtone, sometimes it can be an almost mauve grey shade. Black Opal has dark to jet black body colour although sometimes this is not very apparent.
Boulder Opal comes from Queensland, in the past it was thrown out as worthless and useless, it is now a great favourite with many collectors and jewellery designers. It can also be quite an affordable way of collecting some nice Opal. The Opal forms in crevices in the ironstone, it can be seen as veins running through the rock or covering the face of it when it is usually referred to as boulder Opal but sometimes the ironstone is mixed in with the pattern on the face of the stone this is known as Opal in Matrix or Matrix Opal.
Another affordable way to buy some nice Opal is in a doublet or triplet. Doublets have a thin slice of precious Opal cemented to a base of ironstone, onyx or some other dark material, Triplets are essentially doublets with the addition of a transparent layer on top of the Opal such as quartz. When doublets are mounted in jewellery it is often quite difficult to tell that they are not solid opal if the setting covers the ironstone!
Australia’s Opal fields are in three states, New South Wales, Queensland and South Australia, along the Great Artesian Basin an ancient inland sea.
Some of the best known Opal mines for white Opal are the Coober Pedy fields. Many local people live in dugouts as it is a desert region with low rainfall living underground makes for cool living in the summer warm in the winter.
Andamooka, mines are deep down on an ancient sea bed, where Opalised shells, stones and even dinosaur bones are being dug up as well as the more usual type of Opal.
Mintubi fields have a harsh climate mining is done in the open – cut system, black Opal has also been found here.
I have some beautiful Mintubi crystal Opal.
Lambina produces a major portion of Australia’s Opal, I have just been fortunate enough to buy some Lambina Opals.
White Cliffs, in north western New South Wales produces mainly white or crystal Opal. (no photo available)
Lightening Ridge in Northern New South Wales is famous for its black Opal.
Boulder Opal is mined in Queensland at Quilpie, Winton, Opalton and Yowah in Yowah the Opalised Ironstone is known as “Yowah Nuts”.
I hope whoever reads this enjoys my little Opal ramble. These gorgeous pictures of fine Opals are courtesy of Australian Opal Mines.