Agate disc pendant (assorted colors supplied) from Brazil.

Agate is a transparent, but sometimes opaque variety of quartz and a sub-variety of chalcedony. The chemical structure of agate is identical to jasper, flint, hornwort 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 current river Dirillo in southern Sicily, where agates and other chalcedones were found. Traditionally, agate was worn as a lucky stone or for healing. Consumables such as buttons were also made from agate. A number of medicinal properties are attributed to agate, such as protection during pregnancy, against headaches, skin disorders and balance disorders. According to various literature, agate belongs to the zodiac signs Aquarius, Taurus, Scorpio and Gemini. Agate compounds form as a solution of silica in cavities in older rocks. The stones can be artificially stained to obtain color combinations that are more vibrant than those found in nature. The important sources of agate are Brazil, Uruguay and the United States (Oregon, Washington and around Lake Upper). 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. Fission: none. Color: light blue or gray but it can also be green Stripe color: none. Gloss: glass gloss, matt, satin gloss. Hardness (Mohs): 6.5 to 7. Average density: 2.65 kg / dm3. Transparency: transparent to translucent.