metamorphic
Tiger's Eye (Blue/Black variety, also known as Hawk's Eye)
Silicified Crocidolite (Silicon Dioxide with inclusions, SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Dark blue-grey to black with silky bands; Luster: Silky; Crystal structure: Trigonal/Fibrous; Cleavage: None/Indistinct; Specific Gravity: 2.64-2.71
- Hardness
- 6
- Color
- Dark blue-grey to black with silky bands
- Luster
- Silky
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Dark blue-grey to black with silky bands; Luster: Silky; Crystal structure: Trigonal/Fibrous; Cleavage: None/Indistinct; Specific Gravity: 2.64-2.71
Formation & geological history
Formed through the pseudomorphism of crocidolite (blue asbestos) by quartz. As quartz replaces the fibers, it retains the parallel fibrous structure, creating chatoyancy. It occurs in regional metamorphic environments.
Uses & applications
Used primarily for jewelry (cabochons, beads), decorative carvings, tumbling for collectors, and in metaphysical practices.
Geological facts
Also known as Hawk's Eye, it is essentially unfinished Tiger's Eye; if the iron levels were higher and oxidized, it would turn the familiar golden-brown color. The 'eye' effect is called chatoyancy.
Field identification & locations
Identify by its characteristic 'chatoyancy' (moving light bands) when rotated. Found commonly in South Africa, Australia, and parts of the USA. Look for silky luster and fibrous appearance even after polishing.
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