Tiger’s eye

The specimen appears to be a polished or tumbled tiger’s-eye cabochon. It is dark brown to golden-brown with a silky, reflective band or chatoyant sheen. Mohs hardness is approximately 6.5–7; luster is vitreous to silky; specific gravity is about 2.64–2.71. It has a trigonal quartz crystal structure, no prominent cleavage, and typically breaks with a conchoidal fracture. The golden banding results from aligned fibrous structures that reflect light as the stone is moved. The image is not sufficient to exclude closely related materials such as hawk’s-eye, brown jasper, or dyed quartz.

Tiger’s eye forms when blue-gray crocidolite fibers are progressively replaced by quartz while retaining the fibrous texture. Iron oxidation produces the characteristic golden-brown color. It is a metamorphic or hydrothermal alteration product rather than a conventional igneous, sedimentary, or metamorphic rock in hand-specimen classification. The material is generally associated with Precambrian rocks, although the exact age depends on the deposit. Major commercial deposits occur in South Africa and Western Australia.

Commonly used for polished cabochons, beads, carvings, worry stones, tumbled stones, and ornamental objects. It is popular in inexpensive to moderately priced jewelry and mineral collections. It has little major industrial or construction use.

The moving band of light is called chatoyancy, from the French word for cat’s eye. Tiger’s eye is part of a related quartz group that includes blue hawk’s-eye and red tiger’s-eye. Red material may be naturally oxidized or artificially heat-treated. The original crocidolite fibers are generally altered and encapsulated within quartz, but dust from cutting or drilling should still be avoided.

Identification clues include a brown-to-golden color, opaque to slightly translucent edges, smooth polish, and a silky line that shifts when the stone is rotated under a single light source. A strong, continuous cat’s-eye band supports tiger’s eye; a blue-gray color suggests hawk’s-eye. A scratch test should be performed only on an inconspicuous area: genuine quartz should not be scratched by a steel knife easily, but it can scratch glass. Confirmatory testing would include refractive index, specific gravity, microscopic examination, and checking for dye or glass bubbles. Common sources include South Africa, Western Australia, India, Namibia, Brazil, and the United States.