Standard for agate slices 10x6.7x2 cm.

Agate is a translucent, but sometimes opaque variety of quartz and a sub-variety of chalcedony. The chemical structure of agate is identical to jasper, flint, chert and is often found together with opal. The colorful, striped specimens are used as gemstones. 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. Consumer articles were also made of agate such as buttons. 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 constellations Aquarius, Taurus, Scorpio and Gemini. Agate compounds form as a solution of silicic acid in cavities in older rocks. The stones can be artificially stained to achieve color combinations more vibrant than those found in nature. The major sources of agate are Brazil, Uruguay and the United States (Oregon, Washington and around Lake Superior). 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. Gloss: glass gloss, matt, semi-gloss. Hardness (Mohs): 6.5 to 7. Average density: 2.65 kg/dm3. Transparency: transparent to translucent.