metamorphic
Blue Tiger's Eye (Hawk's Eye)
Silicified Crocidolite (Pseudomorph of Quartz after Crocidolite), SiO2
Hardness: 6.5–7 on Mohs scale; Color: Blue-gray to blue-green with chatoyant bands; Luster: Silky; Crystal Structure: Trigonal (fibrous aggregate); Cleavage: None; Specific Gravity: 2.64–2.71.
- Hardness
- 6
- Color
- Blue-gray to blue-green with chatoyant bands
- Luster
- Silky
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Blue-gray to blue-green with chatoyant bands; Luster: Silky; Crystal Structure: Trigonal (fibrous aggregate); Cleavage: None; Specific Gravity: 2.64–2.71.
Formation & geological history
Formed when quartz replaces the mineral crocidolite (blue asbestos) through a process of pseudomorphism. Unlike gold tiger's eye, the iron in hawk's eye has not oxidized, preserving the blue color. It is typically found in Precambrian metamorphic rocks.
Uses & applications
Primarily used in jewelry for cabochons, beads, and carvings. Also highly popular as a pocket stone for collectors and in metaphysical practices.
Geological facts
It exhibits a optical phenomenon called chatoyancy (the cat's-eye effect) caused by the parallel reflection of light off the internal fibrous structure. In ancient times, it was often used as an amulet against the 'evil eye'.
Field identification & locations
Identify by moving the stone under a light source to observe the 'shimmering' moving bands. It is commonly found in South Africa (the Griquatown West region), Australia, and Brazil. Collectors should look for high-contrast banding and lack of cracks.
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