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

gemstone A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...

that is usually a metamorphic rock 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 Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

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 Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as , although this is not entirely accurate as the ratio of oxide to hydroxide can vary qu ...

Other forms of tiger's eye

''Tiger iron'' is an altered rock composed chiefly of tiger's eye, red jasper and black

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

. 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 , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...

() 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 brecciated chalcedony containing amphibole fibers and promoted as tiger's eye from Namibia and China.

Sources

Quartz - Tigers-Eye - raw stone from Southafrica

Common sources of tiger's eye include Australia, Burma, India, Namibia, South Africa, the United States, Brazil, Canada, China, Korea and Spain.

Cultural associations

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

evil eye The evil eye is a supernatural belief in a curse brought about by a malevolent glaring, glare, usually inspired by envy. Amulets to Apotropaic, protect against it have been found dating to around 5,000 years ago. It is found in many cultures i ...

. 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 Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

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.

References

External links

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