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

chatoyant In gemology, chatoyancy ( ), also called chatoyance or the cat's eye effect, is an optical reflectance effect seen in certain gemstones. (Historically, the term has applied specifically to gems; in woods and other materials the effect is more ...

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 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 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 Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

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 Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wale ...

composed chiefly of tiger's eye, red

jasper Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to ...

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

hilt The hilt (rarely called a haft or shaft) is the handle of a knife, dagger, sword, or bayonet, consisting of a guard, grip, and pommel. The guard may contain a crossguard or quillons. A tassel or sword knot may be attached to the guard or pomme ...

s. 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 Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

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 prism ...

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

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 Asbestos ( ) is a group of naturally occurring, Toxicity, toxic, carcinogenic and fibrous silicate minerals. There are six types, all of which are composed of long and thin fibrous Crystal habit, crystals, each fibre (particulate with length su ...

, 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 Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

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 monoclinic ...

containing

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 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 cuttin ...

cut to best display their

chatoyance In gemology, chatoyancy ( ), also called chatoyance or the cat's eye effect, is an optical reflectance effect seen in certain gemstones. (Historically, the term has applied specifically to gems; in woods and other materials the effect is more ...

. 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 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". Despit ...

, cymophane, but the overall effect is often unconvincing. Artificial

fibre optic An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

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