metamorphic
Blue Tiger's Eye
Pseudomorph of Quartz after Crocidolite (SiO2)
Hardness: 7 Mohs; Color: Dark blue to blue-gray with silky chatoyancy; Luster: Silky to vitreous; Crystal structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: 2.64-2.71
- Hardness
- 7 Mohs
- Color
- Dark blue to blue-gray with silky chatoyancy
- Luster
- Silky to vitreous
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Physical properties
Hardness: 7 Mohs; Color: Dark blue to blue-gray with silky chatoyancy; Luster: Silky to vitreous; Crystal structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: 2.64-2.71
Formation & geological history
Formed when quartz replaces fibrous crocidolite (blue asbestos) crystals while maintaining the fibrous structure. During the metamorphic process, the iron in the crocidolite stays in its original state, keeping the stone blue rather than turning golden-brown.
Uses & applications
Predominantly used as a gemstone for jewelry, carvings, spheres, and tumbled stones for collectors.
Geological facts
Also known as Hawk's Eye or Falcon's Eye. It is a 'pseudomorph', which means 'false form', because quartz took the shape of another mineral during its formation.
Field identification & locations
Identify by the 'cat's eye' effect (chatoyancy) where light reflects off internal fibers. Commonly found in South Africa, Australia, and Brazil. Collectors look for sharp, moving bands of light.
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