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Agates and Jaspers are a crypto-crystalline (crystals too small to be seen even
by a microscope) variety of quartz, known as chalcedony. The varieties of
chalcedony are divided more by character than by color. Chalcedony is divided into
a host of gemstones that have been named for locally common varieties. Some of the
more beautiful types have retained their names on a world-wide basis while other
names have faded into obscurity as many of the relatively small local deposits
became exhausted. Some of the more common of these types are chrysoprase (a pure
green agate), sard (a yellow to brown agate), sardonyx (banded sard), onyx (black
and white agate), carnelian (a yellow to orange agate), flint (a colorful and
microscopically fibrous jasper), jasper (a colorful opaque agate) and bloodstone
(a green with red speckled jasper).
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