An Opal is a mineralid gel which is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl & basalt.
The word ‘Opal’ comes from the Latin word ‘Opalus’. Its origins come from the same source as upala which means stone.
So if you are noodling on the mullock heaps on the outback opal fields of Australia. It doesn’t matter where in Australia you are noodling, be it the Coober Pedy opal fields or the Yowah fields or Koroit or the Ten Mile, there is opal to find, you just have to look. What exactly are you looking for? We all know that it’s a rock with the colours of the rainbow and that it is Australia’s national gemstone and that it’s hard to find. You are looking for the colours of the rainbow in the ground. The predominant colours of opal are red, blue and green, of which red is the most coveted, and over 95% of the world’s opals are found here in this sunburnt country. The less valuable opal is known as potch, or common opal, of which there is much.
Australia has to be the most famous of all countries for the precious stone, the opal. It was first found back in the late 19th century, and this was the well-known and well-prized black opal, although there are many different varieties. The black opal is perhaps the best known and the most valued. It is a little known fact that opal was originally found in a Czechoslovakian mine and dates back to the 14th century, although the Romans also prized this stone, and perhaps this was their source. The various displays of blues, greens, yellows and reds are what make this stone unique, and every stone is different and individual. So unique that each mine is distinctive, and the miner can often identify a stone from his mine when perusing opal jewellery in a jewellery shop ,when the opal has been cut and polished and set into rings, earrings, bracelets and necklaces. It is not a particularly hard stone, so one has to be careful when handling it. It can be brittle and can easily crack if dropped or if treated roughly.
In a nutshell, opal is formed in the spaces between the rocks. It is created when water drips down through silica, very, very slowly in these cavities of volcanic rocks. Shells, bones and wood can also become opalised, which is the same as fossilised, except that these fossils have the opal colour, which makes them exceptional. Opal is formed in the sedimentary rocks of the Great Artesian Basin and is basically a mix of silica dioxide and water formed under pressure. Imagine the water seeping through the sandstone and the smallest particles of silica being picked up via the process. The silica diffracts the light which creates the colours. Keep in mind that your precious opal is only as hard as glass and is quite brittle.
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