metamorphic
Tiger's Eye
Pseudomorph of quartz after crocidolite (SiO2 with iron oxide inclusions)
Hardness: 7 (Mohs scale); Color: Golden to red-brown with silky luster; Crystal structure: Trigonal/Fibrous; Cleavage: None; Specific Gravity: 2.64–2.71. Notable for its chatoyancy (cat's eye effect).
- Hardness
- 7 (Mohs scale)
- Color
- Golden to red-brown with silky luster
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Physical properties
Hardness: 7 (Mohs scale); Color: Golden to red-brown with silky luster; Crystal structure: Trigonal/Fibrous; Cleavage: None; Specific Gravity: 2.64–2.71. Notable for its chatoyancy (cat's eye effect).
Formation & geological history
Formed when quartz replaces fibrous crocidolite (blue asbestos) through a process called pseudomorphism, while maintaining the fibrous structure. Primarily found in iron formations within weathered metamorphic rocks.
Uses & applications
Predominantly used as a gemstone for jewelry (cabochons, beads), decorative carvings, and as a popular specimen for crystal healing and mineral collectors.
Geological facts
The 'chatoyant' effect is caused by the reflection of light off the parallel glass-like fibers within the stone. If the quartz replaces the fibers without oxidizing the iron, the stone remains blue and is known as Hawk's Eye.
Field identification & locations
Identify in the field by its distinct bands of color and the 'moving' light effect when the stone is rotated. Major deposits are found in South Africa (Griqua Town), Western Australia, and Namibia. Collectors should look for sharp, distinct banding without dull patches.
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