Chalcedony
Chalcedony, a general term often applied to varieties of quartz with very fine crystalline structures. Chalcedony quartzes (known technically as cryptocrystalline quartzes) range in color from pale gray to brown, red, blue, green, and black. They have a translucent, waxy appearance and are often marked with veins, spots, or bands. Some varieties are cut and polished for use as semiprecious gems. Agate, bloodstone, carnelian, chert, chrysoprase, flint, jasper, onyx, and certain types of petrified wood are chalcedony quartzes.
Chalcedony is named for the ancient Greek town of Chalcedon in Asia Minor, situated in a region where stones of this type were found. Deposits of chalcedony quartzes are widespread throughout the world.