Black Chalcedony

Okay, if you want to call it black onyx, go ahead. Everybody else in the industry does. But by definition, onyx should have straight parallel stripes of black and white … and these gems don't. The stone is chalcedony, a cryptocrystalline—or microcrystalline—quartz. Examples of chalcedonies of just one color are chrysoprase, a yellowish-green; carnelian, a brownish-orange; and chrysocolla, a greenish-blue. Pure black chalcedony is rare. Most chalcedony is multicolored and banded and is called agate. Other multicolored chalcedonies include bloodstone, the March birthstone, which shows red splotches on a green background. What is onyx? There are two traditional onyxes: black onyx (black and white parallel-striped chalcedony) and sardonyx (orangey-brown and white striped chalcedony). When those bands are wavy, curved, or irregular, the chalcedony is called agate. Because chalcedo
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