chalcedon

n.; pl. Chalcedonies [ L. chalcedonius, fr. Gr. CHalkhdw`n Chalcedon, a town in Asia Minor, opposite to Byzantium: cf. calcédoine, OE. calcidoine, casidoyne. Cf. Cassidony. ] (Min.) A cryptocrystalline, translucent variety of quartz, having usually a whitish color, and a luster nearly like wax. [ Written also calcedony. ] [ 1913 Webster ]

☞ 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. [ 1913 Webster ]