The Probert Encyclopaedia of Rocks & Minerals

CHALCEDONY

Chalcedony is a cryptocrystalline, translucent variant of quartz comprised of silica, having usually a whitish colour, and a lustre nearly like wax.
Chalcedony was named after Chalkedon, near Istanbul. It was traditionally used for decorative objects and amulets. It has a relative hardness of 7. When chalcedony is variegated with spots or figures, or arranged in differently coloured layers, it is called agate; and if by reason of the thickness, colour, 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.
Research Chalcedony