White plume agate "Moon" hand cut from Indonesia.

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, hornet 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 chalcedony were found. Traditionally, agate was worn as a lucky stone or for healing. Consumables were also made of agate such as buttons. Agate has a number of medicinal properties, 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 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.