Chalcedony is one of the
cryptocrystalline varieties of the
mineral quartz, having a waxy lustre. It may be semitransparent or translucent and is usually white to gray or grayish-blue or some shade of brown, sometimes nearly black. Other shades have been given different names. A clear red chalcedony is known as
carnelian or
sard[?]; a green variety colored by
nickel oxide is called
chrysoprase[?].
Prase[?] is a dull green.
Plasma is a bright to emerald-green chalcedony which is sometimes found with small spots of
jasper resembling
blood drops; it has been referred to as
blood stone[?] or
heliotrope[?]. The term chalcedony is derived from the
Greek word meaning
Chalkedon[?], a town in
Asia Minor.
See also: list of minerals