Agate tea light holder, 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 that of jasper, flint and chert, and it is often found together with opal. People use the colourful, striped specimens 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 chalcedony were found. People traditionally wore agate as a lucky stone or for healing purposes. Agate was also made into consumer items, such as buttons. Many medicinal properties, including protection against headaches, skin conditions, and balance disorders, are associated with agate. According to various literary works, agate belongs to the zodiac signs Aquarius, Taurus, Scorpio, and Gemini. Agate compounds are formed from a solution of silicic acid that fills cavities in older rocks. You can artificially stain the stones to achieve more vibrant colour combinations than those 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 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/dm³ Transparency: transparent to translucent