The internal colors of valuable opal, birthstone for October, are caused by light passing through silica spheres. Most opal, together with the famous and highly prized black opal, is mined in Australia.
Valuable opal, birthstone for October, is composed of silica spheres. Light passing through the micro-structure of the stone produces various internal colors. There are kinds of opal other than precious, some of which can be of gem quality, these include milky opal, Peruvian blue opal, fire opal and opalized wood, in which the organic structure of the wood has been replaced by opal. In technical terms, opal is a mineraloid gel with a moderately high water content.
Most valuable opal today is mined in Australia, but there are other sources including the Czech Republic, Slovakia, Hungary, Turkey, Indonesia, Brazil, Central America and Ethiopia. In the US it can be found in Spencer, Idaho. NASA reports that opal has been founded on Mars.
Although opals were prized in Europe from the time by the ancient Greeks and Romans, the European market was ruined for fifty years when Sir Walter Scott published a novel about an opal that brought bad luck. It took the discovery of black opals in Australia to bring this stone back to popularity. Queen Victoria laughed at the superstition and gave away opals freely as gifts. Throughout most of its history, opal has been considered good fortune, a position that it occupies in today’s world of gems.
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