A cryptocrystalline, translucent variety of quartz, having usually a whitish color, and a luster nearly like wax.
Fine grain verity of Quartz often deposited as a secondary filler of voids in volcanic rocks, such as cavities and fissures. Found in almost every color. Tends to be translucent in light colors to opaque as colors become darker. Agate, jasper, flint and chert are interchangeable forms of chalcedony. Red color is produced by hematite, gray and black by ferric iron or organic carbon.