Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Tiger's Eye is a captivating gemstone known for its striking chatoyancy, a silky, luminous band of reflected light that moves across the surface as the stone is rotated. It is a variety of chalcedony, which is a cryptocrystalline form of silica (SiO2). The characteristic golden-yellow to reddish-brown colors are due to the presence of iron oxides, particularly goethite, which has replaced the original fibrous crocidolite asbestos. The fibrous structure of the original mineral is preserved, giving Tiger's Eye its distinctive appearance.
How to Identify
- Color
- Golden-yellow, golden-brown, reddish-brown, sometimes blue (Hawk's Eye). The colors are typically banded or streaked.
- Luster
- Silky to vitreous, exhibiting strong chatoyancy.
- Texture
- Fine-grained, fibrous appearance due to the pseudomorphic replacement. Often polished smooth for display.
- Crystal Form
- Massive, fibrous aggregates, typically found in veins. Does not form macroscopic crystals.
- Cleavage
- None, due to its cryptocrystalline nature and fibrous replacement.
- Geological Environment
- Formed in veins within iron-rich metamorphic rocks, where crocidolite asbestos has been replaced by silica and iron oxides. Often found in serpentinite or other ultramafic rocks that have undergone metamorphism.
Key Facts
- Hardness: 6.5-7 on the Mohs scale
- Specific Gravity: 2.64-2.71
- Crystal System: Trigonal (cryptocrystalline)
- Color: Golden-yellow, golden-brown, reddish-brown, blue (Hawk's Eye)
- Luster: Silky to vitreous, chatoyant
- Transparency: Opaque to translucent
- Fracture: Conchoidal to splintery
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with inclusions of iron oxides (goethite) and relict fibrous structure of crocidolite.
Quick Check
- Color: Golden-yellow to reddish-brown, sometimes blue
- 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, vitreous
Formation
Tiger's Eye is a pseudomorph of quartz after crocidolite. Crocidolite, a fibrous blue asbestos mineral, forms in veins within iron-rich metamorphic rocks. Over time, silica-rich hydrothermal fluids infiltrate these veins. The silica replaces the crocidolite fibers while preserving their original fibrous structure. Iron oxides (primarily goethite) then stain the silica, creating the characteristic golden-brown to reddish-brown colors and the chatoyancy (cat's-eye effect). The chatoyancy is caused by the parallel alignment of the original crocidolite fibers, now replaced by quartz, which reflects light in a silky band.
Usage
Primarily used as a gemstone for jewelry (cabochons, beads, carvings), ornamental objects, and decorative items. Its unique chatoyancy makes it highly prized.
Age Distribution
Formed over geological timescales, typically associated with ancient metamorphic events.
Where to Find
South Africa
The primary and most significant source of high-quality Tiger's Eye, particularly in the Griqualand West region of the Northern Cape Province. Deposits are found in banded iron formations.
Australia
Significant deposits are found in Western Australia, often associated with banded iron formations.
India
Smaller deposits are known, contributing to the global supply.
Myanmar (Burma)
Some occurrences have been reported.
United States
Limited occurrences in states like Arizona and California.
Finding Tips
Look for Chatoyancy
The most distinctive feature is the moving band of light. Rotate the specimen under a light source to observe this effect. This is crucial for identification.
Observe Color and Pattern
Tiger's Eye typically displays golden-yellow to reddish-brown colors, often with parallel bands or streaks. Blue varieties (Hawk's Eye) also exist.
Check Hardness
With a Mohs hardness of 6.5-7, it will scratch glass and steel. This helps differentiate it from softer imitations.
Examine Texture (if unpolished)
Unpolished specimens may show a fine, fibrous texture, indicative of its pseudomorphic origin.
Consider Geological Context
If found in situ, it will likely be in veins within iron-rich metamorphic rocks, often associated with banded iron formations.
Similar Rocks
Hawk's Eye
Hawk's Eye (a variety of Chalcedony)
Also known as: Blue Tiger's Eye
Pietersite
Pietersite (a variety of Chalcedony with embedded crocidolite fibers)
Also known as: Tempest Stone
Cat's Eye Chrysoberyl
Chrysoberyl (BeAl2O4)
Also known as: Cymophane
Scientific Classification
- Mineral Class
- Silicates (Tectosilicates)
- Group
- Quartz Group (Chalcedony variety)
- Crystal System
- Trigonal (cryptocrystalline)
- Chemical Formula
- SiO2 (with fibrous inclusions of altered crocidolite and iron oxides)
- Composition
- Silicon dioxide, with iron oxide (goethite) responsible for color and chatoyancy. The fibrous structure is a pseudomorph of crocidolite (Na2(Fe2+,Mg)3Fe3+2Si8O22(OH)2).
Explore Tiger's Eye
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.