metamorphic
Tiger's Eye (with Blue Tiger's Eye / Hawk's Eye)
Pseudomorph of Quartz after Crocidolite (SiO2 with inclusions)
Hardness: 6.5–7 (Mohs); Color: Golden brown, yellow, and blue-gray; Luster: Silky; Crystal structure: Trigonal (fibrous); Cleavage: None (fractures); Specific gravity: 2.64–2.71
- Hardness
- 6
- Color
- Golden brown, yellow, and blue-gray
- Luster
- Silky
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Physical properties
Hardness: 6.5–7 (Mohs); Color: Golden brown, yellow, and blue-gray; Luster: Silky; Crystal structure: Trigonal (fibrous); Cleavage: None (fractures); Specific gravity: 2.64–2.71
Formation & geological history
Formed when quartz replaces the fibrous mineral crocidolite (blue asbestos) through a process called pseudomorphism. Pressure and heat during regional metamorphism facilitate this change, often found in Precambrian formations over 2 billion years old.
Uses & applications
Primarily used in jewelry (cabochons, beads), decorative carvings, and as a popular specimen for metaphysical and rock collectors.
Geological facts
The 'chatoyancy' or cat's-eye effect is caused by the light reflecting off the parallel fibers of the minerals. When the quartz replacement is incomplete, mineral remains blue, creating 'Hawk's Eye'.
Field identification & locations
Identify by its distinct silky luster and 'moving' bands of light when rotated under a light source. Found commonly in South Africa, Australia, and Namibia. Collectors should look for high contrast and sharp chatoyant bands.
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