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Tiger's eye

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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 color, 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

Unpolished Tiger eye from South Africa

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 colors 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 fiberoptic glass is a common imitation of tiger's eye, and is produced in a wide range of colors. Tiger's Eye mostly comes from South Africa and East Asia.

Tiger iron

Tiger iron

Tiger iron is an altered rock composed chiefly of tiger's eye, red jasper, and black hematite. The undulating, contrasting bands of color and luster make for an attractive motif, and it is mainly used for jewelry-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 colored 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

Serpentine tiger's eye from Arizona

Arizona and California have serpentine deposits in which are occasionally found chatoyant bands of chrysotile fibers. 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.  
  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.  

External links

  • GSA Comment and Reply on formation of Tiger's and Hawk's Eye
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