Agate slices on stand found around 1950-1955 from the Salto do Jacuí mine in Brazil

Agate is a transparent, but sometimes opaque variety of quartz and a subvariety of chalcedony. The chemical structure of agate is identical to that of jasper, flint and chert, and it is often found together with opal. The colourful, striped specimens are used as a semi-precious stone. The name agate comes from the Greek Ἀχάτης, Achatès, the name of the present-day Dirillo River in southern Sicily, where agates and other chalcedony were found. Traditionally, agate was worn as a lucky stone or for healing. Agate was also made into consumer items, such as buttons. Agate is attributed with a number of medicinal properties, such as protection during pregnancy, against headaches, skin conditions 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 silicic acid in cavities in older rocks. The stones can be artificially stained to obtain colour combinations that are more vibrant than those found in nature. The main 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, trigona Cleavage: none. Colour: light blue or grey, but it can also be green Streak colour: none Luster: vitreous, matt, satin Hardness (Mohs): 6.5 to 7. Average density: 2.65 kg/d Transparency: transparent to translucent