metamorphic
Tiger's Eye (specifically Blue Tiger's Eye / Falcon's Eye)
Pseudomorph of Quartz after Crocidolite (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Blue-gray to golden brown; Luster: Silky; Crystal structure: Trigonal (fibrous texture); Cleavage: None; Specific Gravity: 2.64–2.71
- Hardness
- 6
- Color
- Blue-gray to golden brown
- Luster
- Silky
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Blue-gray to golden brown; Luster: Silky; Crystal structure: Trigonal (fibrous texture); Cleavage: None; Specific Gravity: 2.64–2.71
Formation & geological history
Formed when quartz replaces the fibrous mineral crocidolite (asbestos) through a process called pseudomorphism. Pressure and heat during metamorphism create the chatoyant 'cat's eye' effect. Most deposits are Proterozoic in age (approx. 2 billion years old).
Uses & applications
Primarily used as a gemstone in jewelry (cabochons, beads), decorative carvings, and as a popular specimen for crystal collectors and lapidaries.
Geological facts
The characteristic shimmer is known as 'chatoyancy.' While golden tiger's eye is more common, the blue variety (Falcon's Eye) represents an earlier stage of the mineral's development before the iron in the crocidolite has oxidized.
Field identification & locations
Identify in the field by its distinctive silky luster and fibrous 'banded' appearance that shifts when viewed from different angles. It is most commonly found in the Griqualand West region of South Africa and the Hamersley Range in Western Australia.
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