chalcedony

chalcedony [from Chalcedon ], form of quartz the crystals of which are so minute that its crystalline structure cannot be seen except with the aid of a microscope. Chalcedony has a waxy luster and is translucent to transparent. The name chalcedony is applied more specifically to white, gray, blue, and brown varieties. Some varieties, differing in color because of the presence of impurities, are agate , bloodstone, carnelian , chrysoprase, jasper , onyx , sard, and sardonyx.

chalcedony Microcrystalline form of quartz. When cut and polished, it is used by gem engravers. It is waxy, lustrous and there are white, grey, blue and brown varieties. Often coloured by artificial methods, some varieties contain impurities giving a distinctive appearance, such as agate (coloured bands), onyx (striped) and bloodstone (dark green with red flecks).

chalcedony a microcrystalline type of quartz occurring in several different forms including onyx and agate. The word comes (in late Middle English) from Latin chalcedonius (often believed to mean ‘stone of Chalcedon’, but this is doubtful), which in the Vulgate represents Greek khalkēdōn, the name (in Revelation 21:19) of the precious stone forming the third foundation of the New Jerusalem.