Agate pair quality A, in various colors, from Brazil.

Agate is a transparent, but sometimes also opaque, variety of quartz and a sub-variety of chalcedony. The chemical structure of agate is identical to jasper, flint, and hornstone and is often found together with opal. The colorful, striped specimens are used as semi-precious stones. The name agate comes from the Greek Ἀχάτης, Achatès, the name of the present-day Dirillo River in southern Sicily, where agates and other chalcedonies were found. Traditionally, agate was worn as a lucky stone or for healing. Items made of Agate were also created, such as buttons. A number of healing properties are attributed to agate, such as protection during pregnancy against headaches, skin conditions, and balance disorders. According to various literature, agate is associated with the zodiac signs Aquarius, Taurus, Scorpio, and Gemini. Agate formations occur as a solution of silicic acid in cavities in older rocks. The stones can be artificially stained to achieve color combinations that are more vibrant than those found in nature. The major sources of agate are Brazil, Uruguay, and the United States (Oregon, Washington, and around the Great Lakes). Closer to the Netherlands and Belgium, agate is also found in the Hunsrück in Germany. Chemical composition: SiO₂ + Al, Ca, Fe, Mn Crystal system: belongs to chalcedony-like quartz crystals, trigonal. Cleavage: none. Color: light blue or gray, but it can also be green Stripe color: none. Luster: glassy, dull, silky. Hardness (Mohs): 6.5 to 7. Average density: 2.65 kg/dm2. Transparency: transparent to translucent.