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Glossary: Useful Terms Relating To Watches & Jewellery
Obsidian
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A volcanic glass (also called Apache tears) that is usually black, but occasionally red, brown, grey, green (rare), dark with "snowflakes," or even clear. This glassy, lustrous mineral is found in lava flows, and obsidian stones can be massive. Obsidian is formed when viscous lava from volcanoes cools rapidly. Most obsidian is 70 percent silica.
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Onyx
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A semi-precious stone that is black and white, generally arranged in layers. It is a form of agate with parallel banding. Onyx is a species of chalcedony.
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Opals
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Semi-precious stones that are luminous and iridescent, frequently with inclusions of many colours ("fire"). Opal is a mineral composed of noncrystalline (amorphous) silica water, and is a species of quartz. There are three major types of opals: common opal, opalescent precious opal (white or black, with a rainbow-like iridescence caused by tiny crystals of cristobalite), and fire opal (a milky stone that is orange to red in colour with no opalescence).
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Opalescence
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A milky white/blue type of iridescence.
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Orient
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The deep, inner glow and shimmering iridescent characteristics of sea-grown pearls. The deeper the lustre and iridescence, the more precious the pearl.
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