Chalcedony semiprecious gemstone index and mineral information

Chalcedony is a variety of microcrystalline quartz (silicon dioxide), often with some iron and aluminum.  It is composed of microscopic fibers.  Chalcedony is found in veins, geodes, and concretions.  It can be mammillary, botroyoidal, or stalactitic.  Chalcedony is found in numerous locations throughout the world.

Its name may derive from the ancient port of Khalkedon in Asia Minor known today as (Turkey).

The word Chalcedony covers a group of quartzes, including agate, petrified wood, chrysophrase, bloodstone, jasper, carnelian, moss agate, and sard.  When pure, chalcedony has its own distinct properties.  It is translucent and has a white or bluish color, but it may be colored green by chromium. Chalcedony is formed in several environments, generally near the surface of the earth where temperatures and pressures are relatively low.

Apple-green chalcedony is called chrysoprase; dark red or orange-red to reddish brown chalcedony is called carnelian; dark green spotted with red inclusions is called heliotrope (bloodstone); distinctly banded specimens, in which adjacent bands differ in color and in degree of translucency, are called agate; and mottled yellow, red, brown, or green chalcedony is called jasper.

Good quality chalcedony is found in Brazil, India, Madagascar and Uruguay.  Its fibrous structure gives chalcedony its toughness and makes it ideal for carving, especially in Germany where it is very popular.  Because of its porous consistency, it may be dyed with a variety of metallic salts.

Mohs’ hardness: 6.5 – 7