metamorphic
Tiger's Eye (Brown/Dark variety)
Pseudomorph of Quartz after Crocidolite (SiO2 with inclusions)
Hardness: 7 on Mohs scale; Color: Dark brown to golden-yellow; Luster: Silky to sub-vitreous; Crystal structure: Trigonal (fibrous aggregate); Cleavage: None; Specific gravity: 2.64-2.71; Chatoyancy (cat's eye effect) visible when moved under light.
- Hardness
- 7 on Mohs scale
- Color
- Dark brown to golden-yellow
- Luster
- Silky to sub-vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown to golden-yellow; Luster: Silky to sub-vitreous; Crystal structure: Trigonal (fibrous aggregate); Cleavage: None; Specific gravity: 2.64-2.71; Chatoyancy (cat's eye effect) visible when moved under light.
Formation & geological history
Formed when quartz replaces the fibrous mineral crocidolite (blue asbestos) through a process of pseudomorphism. The iron from the original crocidolite oxidizes, turning the blue fibers into the characteristic brown/gold hues. Often found in Precambrian iron formations.
Uses & applications
Primarily used in jewelry (cabochons, beads), decorative carvings, and as a popular specimen for rock collectors and metaphysical practitioners.
Geological facts
Tiger's Eye is a 'pseudomorph,' meaning it has the chemical composition of one mineral (quartz) but retains the physical shape and fibrous structure of a different mineral (crocidolite). Roman soldiers supposedly wore it for protection in battle.
Field identification & locations
Identify by its 'chatoyancy'—the way the light reflects off the parallel fibers to create a moving band of light. Commonly found in South Africa (Northern Cape), Australia, Myanmar, and India. Collectors should look for high-contrast bands and a smooth, silky finish.
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