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Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the
minerals quartz and moganite[2]. These are both silica minerals, but they differ in that quartz
has a trigonal crystal structure, whilst moganite
is monoclinic.
Chalcedony has a waxy lustre, and may be semitransparent
or translucent. It can assume a wide range of colors, but those most commonly
seen are white to gray, grayish-blue or a shade of brown ranging from pale to
nearly black.
Chalcedony and its named varieties are well
represented in various birthstone charts and can be found for all the months
except January, April, and November. It is also listed as a birthstone for all
the Zodiac signs except Taurus, Cancer, Scorpio and Sagittarius.
The term chalcedony is derived from the name of
the ancient Greek town Chalkedon in Asia
Minor.
Chalcedony, which is found worldwide, is the
name for a group of stones made of a microcrystalline or cryptocrystalline
variety of quartz, which means the quartz crystals are too small to be seen
without high magnification.
Chalcedony is found in almost every color including:
white, gray, black, brown, brownish red, orange, yellow, light to dark green,
blue, lavender or, in the case of agates and jaspers, combinations of those
colors |