metamorphic
Tiger's Eye (Golden and Blue Pietersite mix)
Pseudomorph of Quartz after Crocidolite (SiO2 with iron inclusions)
Hardness: 6.5–7 (Mohs scale); Color: Golden brown, amber, and deep blue/black; Luster: Silky; Crystal structure: Trigonal (fibrous); Cleavage: None; Specific gravity: 2.64–2.71.
- Hardness
- 6
- Color
- Golden brown, amber, and deep blue/black
- Luster
- Silky
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Golden brown, amber, and deep blue/black; Luster: Silky; Crystal structure: Trigonal (fibrous); Cleavage: None; Specific gravity: 2.64–2.71.
Formation & geological history
Formed through the pseudomorphism of crocidolite (asbestos) by silica. The fibers of the asbestos are replaced by quartz while retaining the fibrous structure, creating chatoyancy. It is typically found in Precambrian rocks approximately 2 to 3 billion years old.
Uses & applications
Used primarily in jewelry (cabochons, beads), decorative carvings, and as a popular collector's gemstone for its optical 'cat's eye' effect.
Geological facts
The shifting light effect is called chatoyancy. In ancient times, it was carried as an amulet against curses and used by Roman soldiers to provide courage in battle. The 'Blue' variety seen in parts of the specimen is often called Hawk's Eye.
Field identification & locations
Identify in the field by its distinct chatoyant 'moving' bands of light when rotated and its fibrous texture under a high-shine polish. Common locations include South Africa (Northern Cape), Western Australia, Namibia, and Brazil.
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