Chalcedony

Chalcedony is a cryptocrystalline form of silica, composed of very fine inter growths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic.

Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colour, but those most commonly seen are white to grey, greyish-blue or a shade of brown ranging from pale to nearly black.

The name chalcedony comes from the Latin chalcedonius (alternatively spelled calchedonius). The name appears in Pliny the Elder’s Naturalis Historia as a term for a translucid kind of Jaspis. The name is probably derived from the town Chalcedon in Asia Minor.