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Tiger's Eye is a captivating pseudomorph of quartz, meaning one mineral (quartz) has replaced another (crocidolite) while retaining the original mineral's external form. Its most distinctive feature is its chatoyancy, a silky, luminous streak of light that moves across the surface as the stone is rotated. The 'gold' variety exhibits a rich golden-brown to reddish-brown color, often with iridescent bands. The 'blue' variety, known as Hawk's Eye or Falcon's Eye, displays shades of blue-gray to blue-green. Both varieties can occur together, creating a striking contrast. The fibrous structure, inherited from the original crocidolite, is responsible for the optical effect.
How to Identify
- Color
- Golden-brown to reddish-brown (gold Tiger's Eye); blue-gray to blue-green (blue Tiger's Eye/Hawk's Eye). Often banded or streaked.
- Luster
- Silky to vitreous, with a distinct chatoyancy.
- Texture
- Fine-grained, fibrous appearance, often with a smooth, polished feel when cut and polished.
- Crystal Form
- Massive, fibrous aggregates, pseudomorphing original crocidolite fibers. Does not typically form macroscopic crystals of quartz.
- Cleavage
- None, as it is a cryptocrystalline variety of quartz.
- Geological Environment
- Formed in metamorphic environments, typically within banded iron formations or other iron-rich sedimentary rocks, where crocidolite asbestos was originally present.
Key Facts
- Hardness: 7 (Mohs scale)
- Specific Gravity: 2.64 - 2.71
- Crystal System: Trigonal (cryptocrystalline)
- Color: Golden-brown, reddish-brown, blue-gray, blue-green
- Luster: Silky, vitreous, chatoyant
- Transparency: Opaque to translucent
- Fracture: Conchoidal to splintery
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with fibrous inclusions of iron oxides (limonite/goethite) or unoxidized crocidolite.
Quick Check
- Color: Golden-brown, reddish-brown, blue-gray, blue-green
- Luster: Silky, chatoyant
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, fibrous aggregates, pseudomorphic after crocidolite.
- Cleavage Type: None
- Fracture Type: Conchoidal to splintery
- Tenacity: Brittle
- Luster Type: Silky to vitreous, with strong chatoyancy
Formation
Tiger's Eye forms through a pseudomorphic replacement process. Initially, fibrous crocidolite (a blue asbestos mineral, specifically a variety of riebeckite, Na2(Fe2+3Fe3+2)Si8O22(OH)2) crystallizes within fractures in host rocks, often banded iron formations. Hydrothermal fluids then introduce silica, which gradually replaces the crocidolite fibers while preserving their original fibrous structure. The iron content within the original crocidolite oxidizes during this process, leading to the characteristic golden-brown color of classic Tiger's Eye (due to limonite or goethite inclusions). Blue Tiger's Eye, or Hawk's Eye, represents an earlier stage of this replacement where the crocidolite has not fully oxidized, retaining its original blue-gray to blue-green color. The chatoyancy (cat's-eye effect) is a result of light reflecting off the parallel fibrous inclusions.
Usage
Primarily used as a gemstone for cabochons, beads, carvings, and ornamental objects due to its attractive chatoyancy and color. It is also popular in jewelry. Historically, it was believed to offer protection and bring good fortune.
Age Distribution
Typically Precambrian to Paleozoic, depending on the host rock formation.
Where to Find
South Africa
The primary and most historically significant source, particularly in the Griqualand West region, where vast deposits of both golden and blue Tiger's Eye are found within banded iron formations.
Australia
Western Australia, particularly the Hamersley Range, is another important source, producing high-quality material.
India
Smaller deposits are known, contributing to the global supply.
Myanmar (Burma)
Some occurrences have been reported.
United States
Limited occurrences in certain states, but not a major commercial source.
Finding Tips
Look for Chatoyancy
The most definitive characteristic is the moving band of light. Rotate the specimen under a light source to observe this effect.
Observe Color and Pattern
Note the characteristic golden-brown, reddish-brown, or blue-gray to blue-green colors, often with parallel bands or streaks.
Check for Fibrous Structure
Even though it's quartz, the pseudomorphic nature means you might discern a fine fibrous texture, especially on unpolished surfaces or under magnification.
Consider Hardness
As a quartz variety, it should be able to scratch glass (Mohs hardness 7).
Geological Context
If collecting in situ, look for it in metamorphic terrains associated with banded iron formations.
Similar Rocks
Cat's Eye Chrysoberyl
Chrysoberyl (BeAl2O4)
Also known as: Cymophane
Serpentine Cat's Eye
Serpentine Group Minerals
Also known as: Bowenite Cat's Eye
Pietersite
Chalcedony with embedded crocidolite fibers
Also known as: Tempest Stone
Scientific Classification
- Mineral Class
- Silicate (Tectosilicate)
- Group
- Quartz Group
- Crystal System
- Trigonal (cryptocrystalline)
- Chemical Formula
- SiO2 (with inclusions)
- Composition
- Silicon dioxide with fibrous inclusions of iron oxides (limonite/goethite) for golden varieties, or unoxidized crocidolite (Na2(Fe2+3Fe3+2)Si8O22(OH)2) for blue varieties.
Explore Tiger's Eye (Blue and Gold)
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