Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Varieties of Chalcedony include, Agate, Aventurine, Bloodstone, Carnelian, Chrysoprase, Jasper, Onyx, Sard and Sardonyx.

Chalcedony is found in South Africa, Namibia, Zimbabwe and Swaziland.