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About Minerals

Tiger's Eye

This is a variety of quartz which owes its name to the banded yellow-gold, dark brown color which resembles a tiger's eye. It occurs in veins, parallel to bedding, usually less than 6 cm thick. Historically the origin is considered to be an example of peudomorphism - the replacement of one mineral by another which retains the form of the original. In this case, crocidolite is replaced by quartz. Crocidolite (asbestos)..... gives this material its chatoyance. The quartz retains the original fibrous structure. The resultant yellow to brown color is from iron oxide staining-unstained pieces or areas retain the original blue color and are called hawk's eye.

The replacement theory has recently been challenged and now researchers believe it is a crack/seam filling. Mineral rich fluids infiltrate a pre-existing crack in the rock and deposit the quartz. This shows a distinctive, fibrous growth pattern extending from the edge of each side toward the center, sealing the crack. Crocidolite fibers are still present but occur as inclusions within the quartz and are believed to grow from fragments originally present on the crack edges. The characteristic color is still caused by iron oxide stain and the fibrous texture produces the characteristic iridescent luster or chatoyance.

Regardless of which origin you favor, tiger's eye is always linked to crocidolite and therefore only occurs where deposits of crocidolite are found - South Africa, Western Australia, China, and South America. The uses of tiger's eye and hawk's eye are as gems, most commonly as cabochons. However, excellent carvings have been produced from this material;. Also, it plays a significant role in holistic procedures and astrology.

( derived from an article by Frank Craig that appeared in Rock Buster News 8/13)