Chalcedony
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Chalcedony is one of the cryptocrystalline varieties of the mineral quartz, having a waxy luster. Chalcedony may be semitransparent or translucent and is usually white to gray, 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 and onyx is black and white banded. Plasma is a bright to emerald-green chalcedony that is sometimes found with small spots of jasper resembling blood drops; it has been referred to as blood stone or heliotrope. Flint is also a variety of chalcedony.
People living along the Central Asian trade routes used various forms of chalcedony, including carnelian, to carve intaglios, ring bezels (the upper faceted portion of a gem projecting from the ring setting), and beads that show strong Graeco-Roman influence. Fine examples of first century objects made from chalcedony, possibly Kushan, were found in recent years at Tillya-tepe in north-western Afghanistan. Hot wax would not stick to it so it was often used to make seal impressions.
The term chalcedony is derived from the name of the ancient Greek town Chalkedon in Asia Minor, in modern English usually spelled Chalcedon.
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de:Chalcedon (Mineral) et:Kaltsedon fr:Calcédoine pl:Chalcedon (minerał) pt:Calcedônia sk:Chalcedón tr:Kalsedon