Tiger's eye (also called tiger eye) is a chatoyant gemstone that is usually a

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

with a golden to red-brown colour and a silky lustre. As members of the

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

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 Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases,Kostov, R. I. 2010. Review on the mineralogical systematics of jasper and related rocks. – Archaeometry Workshop, 7, 3, 209-213PDF/ref> ...

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 Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

() and is coloured mainly by iron oxide. The

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

ranges from 2.64 to 2.71. It is formed by the alteration of

crocidolite Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long prisma ...

. Serpentine deposits in the US states of Arizona and California can have chatoyant bands of

chrysotile Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in the United StatesOccupational Safety and Health Administration, U.S. Department of Labor (2007)29 C.F.R.&nb ...

, 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

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

ted

chalcedony Chalcedony ( , or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monocli ...

containing amphibole fibers and promoted as tiger's eye from Namibia and China. tiger iron

Sources

Common sources of tiger's eye include Australia, Burma, India, Namibia, South Africa, the United States, Brazil, Canada, China, Korea and Spain. Quartz - Tigers-Eye - raw stone from Southafrica

Quartz - Tigers-Eye - raw stone from Southafrica

Cultural associations

In some parts of the world, the stone is believed to ward off the

evil eye The Evil Eye ( grc, ὀφθαλμὸς βάσκανος; grc-koi, ὀφθαλμὸς πονηρός; el, (κακό) μάτι; he, עַיִן הָרָע, ; Romanian: ''Deochi''; it, malocchio; es, mal de ojo; pt, mau-olhado, olho gordo; ar ...

. Roman soldiers wore engraved tigers eye to protect them in battle.

Cut, treatment and imitation

Gems are usually given a

cabochon A cabochon (; ) is a gemstone that has been shaped and polished, as opposed to faceted. The resulting form is usually a convex (rounded) obverse with a flat reverse. Cabochon was the default method of preparing gemstones before gemstone cutt ...

cut to best display their

chatoyance In gemology, chatoyancy ( ), or chatoyance or cat's eye effect, is an optical reflectance effect seen in certain gemstones, woods, and carbon fibre. Coined from the French "œil de chat", meaning "cat's eye", chatoyancy arises either from the ...

. Red stones are developed by gentle heat treatments. Dark stones are artificially lightened to improve colour using a

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

treatment. Tigers eye egg shape

Honey-coloured stones have been used to imitate the more valued cat's eye

chrysoberyl The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula Be Al2 O4. The name chrysoberyl is derived from the Greek words χρυσός ''chrysos'' and βήρυλλος ''beryllos'', meaning "a gold-white spar". Despite ...

, 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.

References

External links

"New interpretation of the origin of tiger's-eye: Comment and Reply"
. {{Silica minerals Quartz gemstones