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Description
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Opal is a hydrated from of silica, deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock. It is most commonly found in limonite, sandstone, rhyolite, marl, and basalt. The color and opalescence depends on the size and arrangement of the silica making up the opal.
For example, if the size of the silica is small and arranged in a ordinary manner, the opal will have a small range of opalscence, the color blue from purple. If the silica is arranged in an irregular manner, there would be no color.
In a country busy with earthquakes, Japan, most opals turn out to be low quality noble opal because the arrangement of the silica is easily distorted by vibration. On the other hand, in earthquake free countries like Mexico, many high quality fire opals are produced. Since opal is deposited at a relatively low temprature, it is weak against and arid and hot places. During storage it is essential to keep opal in a humid area.
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Opal
