This article is about the gemstone. For the horse eye color, see Tiger eye. For the short story, see The Tiger's Eye. For the characters in the Sailor Moon series, see Amazon Trio.
Tiger's eye (also called tiger eye) is a
chatoyantgemstone that is usually a metamorphic rock with a golden to red-brown colour and a silky lustre. As members of the quartz group, tiger's eye and the related blue-coloured mineral hawk's eye gain their silky, lustrous appearance from the parallel intergrowth of quartz crystals and altered amphibole fibres that have mostly turned into limonite.
Other forms of tiger's eye
Tiger iron is an altered rock composed chiefly of tiger's eye, red jasper and black hematite. The undulating, contrasting bands of colour and lustre make for an attractive motif and it is mainly used for jewellery-making and ornamentation. Tiger iron is a popular ornamental material used in a variety of applications, from beads to knife hilts.
Tiger iron is mined primarily in South Africa and Western Australia. Tiger's eye is composed chiefly of silicon dioxide (SiO2) and is coloured mainly by iron oxide. The specific gravity ranges from 2.64 to 2.71. It is formed by the alteration of crocidolite.
Serpentine deposits in the US states of Arizona and California can have chatoyant bands of chrysotile, a form of asbestos, fibres. These have been cut and sold as "Arizona tiger-eye" and "California tiger's eye" gemstones. The trade name 'pietersite' is used for a fractured or brecciatedchalcedony containing amphibole fibers and promoted as tiger's eye from Namibia and China.
Sources
Common sources of tiger's eye include Australia, India, Myanmar, Namibia, South Africa, the United States, Brazil, Canada, China, Korea and Spain.[citation needed]
Cultural associations
In some parts of the world, the stone is believed to ward off the evil eye.
Roman soldiers wore engraved tigers eye to protect them in battle.
Cut, treatment and imitation
Gems are usually given a cabochon cut to best display their chatoyance. Red stones are developed by gentle heat treatments. Dark stones are artificially lightened to improve colour using a nitric acid treatment.
Honey-coloured stones have been used to imitate the more valued cat's eye chrysoberyl, cymophane, but the overall effect is often unconvincing. Artificial fibre optic glass is a common imitation of tiger's eye, and is produced in a wide range of colours.
Potential hazards
Since 1873, Tiger's eye was thought to be harmless. It was thought that pseudomorphism, meaning that quartz had completely transformed the crocidolite fiber into quartz, leaving no asbestos fibers behind.
In 2003, a new study was performed on the mineralogy of Tiger's Eye. Peter Heaney and Donald Fisher from the Department of Geosciences, at Penn State University. In their study, they discovered that quartz did not fully replace crocidolite. Instead, Tiger's Eye is formed by crack seal crystallization. This involves the crocidolite fibers being fractured continuously on a micro-scale. Later hydrothermal liquids seal the crocidolite fibers in quartz. This means the original crocidolite fibers still exist incased by quartz. Although Tiger's Eye is generally considered safe, the new study shows that grinding, or cutting Tiger's Eye could release small amounts of crocidolite into the air.
Raw and processed tiger's eye
Cut tiger iron slabs at a rock and mineral show. Polished carving in background.
↑Flagg, Arthur Leonard (1958). Mineralogical Journeys in Arizona. Scottsdale: F.H. Bitner. pp.92–93.
↑USGS (1908–1909). "Cat's Eye or Tiger-Eye". Mineral Resources of the United States / Department of the Interior, United States Geological Survey. 2. Washington, D.C.: US Government Printing Office: 802.
