| Chalcedony |
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Information AboutChalcedony |
| CATEGORIES ABOUT CHALCEDONY | |
| minerals | |
| quartz varieties | |
| lithics | |
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Chalcedony is a or Sard . A green variety colored by Nickel Oxide is called Chrysoprase . Prase is a dull green. Onyx has flat black and white bands. ''Plasma'' is a bright to emerald-green chalcedony that is sometimes found with small yellow spots of Jasper . Heliotrope is similar to plasma, but with red spots of jasper, hence its alternative name of ''bloodstone''. Chalcedony with concentric banding is known as Agate . Flint is also a variety of chalcedony. head, 2nd Century AD]] People living along the Central Asia n trade routes used various forms of chalcedony, including Carnelian , to carve Intaglio s, 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 , today the Kadıköy district of Istanbul . GEOCHEMISTRY: CHALCEDONY Chalcedony is more Soluble than quartz under low-temperature conditions, despite the two minerals being chemically identical. This is thought to be due to the fact that chalcedony is extremely finely grained (cryptocrystalline), and so has a very high surface area to volume ratio. SOLUBILITY OF QUARTZ AND CHALCEDONY IN PURE WATER This table gives equilibrium concentrations of total dissolved silicon as calculated by PHREEQC using the llnl.dat database.
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