AGATE
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Written by tom
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Sunday, 02 March 2008 |
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AGATE. A natural mixture of crystalline and colloidal silica, but consisting mainly of the mineral chalcedony. It usually occurs in irregular banded layers of various colors derived from mineral salts, and when polished has a waxy luster.
The specific gravity is about 2.6, and the mineral is sometimes harder than quartz. Agate is used for knife-edges and bearings of instruments, for pestles and mortars, for textile rollers, and for ornamental articles; and the finer specimens are employed as gemstones. The finest of the massive agates come from Uruguay and Brazil. Much agate encloses dendritic, or f`ernlike, pattems of manganese oxide or iron oxide, suggestive of moss. The moss agates of Montana and the yellow green moss agate of California known as amberine are used as gemstones. Agate is a water-deposited stone, and often occurs in the form of stalactites and in petrified wood. Agatized wood of Wyoming and Arizona has a green fluorescence. It is cut into ornaments. Clear translucent yellow agates are called sard, while the clear reddish ones are carnelian. Both are cut as gemstones. Sardoine is a brownish carnelian. Iris agate, with rainbow colors, from Montana and Oregon, is highly prized. Moss opal of Nevada and California is moss agate intergrown with opal. Blue moonstone of California is not a true moonstone but is a blue agate of opalescent luster. Commercial agates may be artificially stained with mineral salts, dyed, or treated with acids to bring out color differences. White agate is a cream-colored chalcedony with a more waxy appearance than agate.
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Last Updated ( Sunday, 02 March 2008 )
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