Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Tiger's Eye is a captivating gemstone known for its silky luster and characteristic chatoyancy, or 'cat's eye' effect. This optical phenomenon is caused by the reflection of light off parallel fibrous inclusions within the stone. The color typically ranges from golden-yellow to reddish-brown, often with alternating bands of lighter and darker hues. It is a variety of chalcedony, which is a cryptocrystalline form of silica, and is essentially silicified crocidolite.
How to Identify
- Color
- Golden-yellow, golden-brown, reddish-brown, sometimes with darker brown or black bands. The color is due to iron oxides.
- Luster
- Silky to vitreous, exhibiting a distinct chatoyancy (a mobile, shimmering band of light).
- Texture
- Fine-grained, fibrous appearance due to the pseudomorphic replacement of crocidolite. Smooth when polished.
- Crystal Form
- Massive, fibrous aggregates. Does not form macroscopic crystals of its own, but rather preserves the fibrous habit of the original crocidolite.
- Cleavage
- None, due to its cryptocrystalline nature. Exhibits conchoidal to splintery fracture.
- Geological Environment
- Typically found in metamorphic rocks, particularly those rich in iron and silica, where crocidolite has undergone silicification. Often occurs in veins or seams within serpentinites or other mafic/ultramafic rocks.
Key Facts
- Hardness: 6.5-7 on the Mohs scale
- Specific Gravity: 2.64-2.71
- Crystal System: Trigonal (as chalcedony, but pseudomorphs fibrous monoclinic crocidolite)
- Color: Golden-yellow, golden-brown, reddish-brown
- Luster: Silky to vitreous, chatoyant
- Transparency: Opaque to translucent
- Fracture: Conchoidal to splintery
- Cleavage: None
- Composition: Silicon dioxide (SiO2) with fibrous inclusions of iron oxides (goethite) and remnants of crocidolite.
Quick Check
- Color: Golden-yellow to reddish-brown with fibrous bands.
- Luster: Silky, chatoyant.
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, fibrous aggregates, pseudomorphing the original crocidolite fibers.
- Cleavage Type: None
- Fracture Type: Conchoidal to splintery
- Tenacity: Brittle
- Luster Type: Silky, chatoyant
Formation
Tiger's Eye is a pseudomorph of quartz after crocidolite (a fibrous amphibole mineral, specifically riebeckite). The formation process involves the replacement of the original crocidolite fibers by chalcedony (microcrystalline quartz) while retaining the fibrous structure. Iron oxides (primarily goethite) are subsequently introduced, staining the quartz and creating the characteristic golden-yellow to reddish-brown colors and the chatoyant effect. This process is a form of silicification.
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 in various geological periods, often associated with Precambrian to Cenozoic metamorphic events where crocidolite was present.
Where to Find
South Africa
The primary and most significant source of Tiger's Eye, particularly in the Griqualand West region, Northern Cape Province. Large deposits are found in the Asbestos Mountains.
Australia
Significant deposits are found in Western Australia, particularly in the Hamersley Range, producing high-quality material.
India
Known for some occurrences, though generally less prominent than South African or Australian sources.
Myanmar (Burma)
Minor occurrences have been reported.
United States
Small deposits found in various states, including Arizona and California.
Canada
Some occurrences have been noted in parts of Canada.
Finding Tips
Look for Metamorphic Terrains
Tiger's Eye is found in areas with significant metamorphic activity, often associated with iron-rich formations and the presence of crocidolite-bearing rocks.
Identify Fibrous Structures
Even in its raw form, look for a distinct fibrous texture. The chatoyancy might be less pronounced before polishing but the parallel fibers should be visible.
Check for Golden-Brown Hues
The characteristic golden-yellow to reddish-brown colors are a key indicator. Hawk's Eye (blue Tiger's Eye) is also found in similar environments.
Examine for Silky Luster
Even on unpolished surfaces, a subtle silky sheen can often be observed, especially when rotated under a light source.
Safety Precaution: Crocidolite
While Tiger's Eye itself is silicified and generally safe, its precursor mineral, crocidolite, is a form of asbestos. When collecting raw, unpolished material, especially in its original geological context, there is a potential risk of encountering un-silicified crocidolite. Avoid disturbing or inhaling dust from such materials. Always wear appropriate respiratory protection (e.g., N95 mask) and eye protection when handling raw, unverified fibrous minerals in the field. Polished Tiger's Eye is considered safe as the asbestos fibers have been replaced by silica.
Similar Rocks
Hawk's Eye
Hawk's Eye (variety of Chalcedony, SiO2)
Also known as: Blue Tiger's Eye
Cat's Eye Chrysoberyl
Chrysoberyl (BeAl2O4)
Also known as: Cymophane
Pietersite
Pietersite (brecciated Tiger's Eye and Hawk's Eye)
Also known as: Tempest Stone
Scientific Classification
- Mineral Class
- Silicates (Tectosilicates)
- Group
- Quartz Group (Chalcedony variety)
- Crystal System
- Trigonal (cryptocrystalline)
- Chemical Formula
- SiO2 (with FeO(OH) inclusions)
- Composition
- Silicon dioxide, with iron oxide (goethite) responsible for color and chatoyancy, and relict fibrous structures of crocidolite.
Explore Tiger's Eye
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.