chalcedony

A large family of minerals. They are quartz, but are translucent to opaque, rather than forming transparent crystals like many quartzes. They are usually not given a faceted cut because they aren't transparent; mostly they are made into cabochons or beads when used in jewelry.
The family contains agate, bloodstone, blue chalcedony, carnelian, chrysoprase, jasper, onyx, petrified wood, prase, sard, and sardonyx.

Chal*ced"o*ny (?), n.; pl. Chalcedonies (#). [ L. chalcedonius, fr. Gr. Chalcedon, a town in Asia Minor, opposite to Byzantium: cf. calc'edoine, OE. calcidoine, casidoyne. Cf. Cassidony.] Min.

A cryptocrystalline, translucent variety of quartz, having usually a whitish color, and a luster nearly like wax.

When chalcedony is variegated with with spots or figures, or arranged in differently colored layers, it is called agate; and if by reason of the thickness, color, and arrangement of the layers it is suitable for being carved into cameos, it is called onyx. Chrysoprase is green chalcedony; carnelian, a flesh red, and sard, a brownish red variety.

© Webster 1913.