MERLINITE CRYSTAL POLISHED SLICE, DENDRITIC CHALCEDONY W.A AUSTRALIA
Chalcedony /kælˈsɛdəni/ is a cryptocrystalline form of silica, composed of very fine intergrowths 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. The standard chemical structure (based on the chemical structure of quartz) is SiO2 (silicon dioxide).
The gem has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black. The color of Chalcedony sold commercially is often enhanced by dying or heating.
The name chalcedony comes from the Latin chalcedonius (alternatively spelledcalchedonius). 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. The Greek word khalkedon (χαλκηδών) also appears in the Book of Revelation(Apc 21,19). It is a hapax legomenon, a word found nowhere else, so it is impossible to tell whether the precious gem mentioned in the Bible is the same mineral known by this name today.
Agate is a variety of chalcedony characterized by either transparency or color patterns, such as multi-colored curved or angular banding. Opaque varieties are sometimes also referred to as Jasper. Fire agate shows iridescent phenomena on a brown background; iris agate shows exceptional iridescence when light (especially pinpointed light) is shone through the stone. Landscape agate is chalcedony with a number of different mineral impurities making the stone resemble landscapes.