Tiger's eye

Tiger's Eye

A photograph showing a polished reddish brown stone which is bisected by a band containing golden fibers

Polished tiger's eye gemstone
General
Category Mineral
Formula
(repeating unit)		 Silica (silicon dioxide, SiO2)
Identification
Color golden to red-brown
Mohs scale hardness 5.5 - 6
Luster Silky
Specific gravity 2.64 – 2.71

Tiger's eye (also called Tigers eye or Tiger eye) is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown colour, with a silky luster. A member of the quartz group, it is a classic example of pseudomorphous replacement by silica of fibrous crocidolite (blue asbestos). An incompletely silicified blue variant is called Hawk's eye.

Cut, treatment and imitation

"Photograph of a chunk of rock containing horizontal bands which contain golden fibers which are positioned vertically within the bands"
Unpolished Tiger eye from South Africa
"Photograph of a polished ovoid stone with bands containing shimmering golden fibers"
Oval shape tiger's eye with iron stripes

The gems are usually cut en cabochon in order to best display their chatoyancy. Red stones are brought about through gentle heat treatment. Dark stones have had their colours improved and been artificially lightened using nitric acid treatments.[1]

Honey-colored stones have been used to imitate the much higher valued cat's eye chrysoberyl (cymophane), but the overall effect is unconvincing. Artificial fibre optic glass is a common imitation of tiger's eye, and is produced in a wide range of colours. Tiger's Eye mostly comes from South Africa and East Asia.

Tiger iron

"Photograph of the surface of a stone which shows horizontal alternating bands of red and black with a band of golden-colored fibers in a band across the center"
Tiger iron

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 -2.71.[2] It is formed by the alteration of crocidolite.

Other forms of tiger's eye

"A photograph of a green stone with a pink fibrous band going across the surface diagonally"
Serpentine tiger's eye from Arizona

Serpentine deposits in which are occasionally found chatoyant bands of chrysotile fibres have been found in the US states of Arizona and California. These have been cut and sold as "Arizona tiger-eye" and "California tiger's eye" gemstones.[3][4] Dark blue-gray fibrous varieties of tiger's eye and hawk's eye is sold under the trade name of Pietersite

Occurrence

Notable sources of tiger's eye include Australia, Burma, India, Namibia, South Africa, United States,[5] Brazil, Canada, China, Korea and Spain.

References

  1. ↑ O'Donoghue, Michael (1997). Synthetic, Imitation, and Treated Gemstones. Boston, Massachusetts: Butterworth-Heinemann. pp. 125–127. ISBN 0-7506-3173-2.
  2. ↑ Listing of SG of gems and gem simulants, Berkeley.edu
  3. ↑ Flagg, Arthur Leonard (1958). Mineralogical Journeys in Arizona. Scottsdale: F.H. Bitner. pp. 92–93.
  4. ↑ USGS (1908–1909). "Cat's Eye or Tiger-Eye". Mineral Resources of the United States / Department of the Interior, United States Geological Survey (Washington, D.C.: US Government Printing Office) 2: 802.
  5. ↑ Schumann, Walter (2009). Gemstones of the World (Fourth ed.). New York, New York: Sterling Publishing. p. 140. ISBN 978-1-4027-6829-3.

External links

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