Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Tiger's Eye is a captivating variety of chalcedony, characterized by its striking chatoyancy, a silky, luminous streak of reflected light that moves across the surface as the stone is rotated. This optical effect is due to the parallel intergrowth of quartz fibers and altered amphibole minerals (primarily goethite, which replaces the original crocidolite fibers). The color typically ranges from golden-yellow to reddish-brown, often with bands of darker brown or black. It is a pseudomorph, meaning it has the external form of one mineral (crocidolite) but the internal composition of another (quartz).
How to Identify
- Color
- Golden-yellow, golden-brown, reddish-brown, sometimes with darker brown or black bands. The color is due to iron oxide inclusions.
- Luster
- Silky to vitreous, exhibiting strong chatoyancy (a moving band of reflected light).
- Texture
- Fibrous appearance internally, but cryptocrystalline (microcrystalline) on a macroscopic scale. Smooth when polished.
- Crystal Form
- Typically massive, occurring in veins or layers. Does not form macroscopic crystals of its own, but retains the fibrous structure of the original crocidolite.
- Cleavage
- None, due to its cryptocrystalline nature. Exhibits conchoidal to splintery fracture.
- Geological Environment
- Found in low-grade metamorphic terrains, often associated with serpentinite or other ultramafic rocks where crocidolite-rich veins have undergone silicification and oxidation.
Key Facts
- Hardness: 6.5-7 on the Mohs scale (due to quartz).
- Specific Gravity: 2.64-2.71 g/cm³.
- Crystal System: Trigonal (as quartz, but cryptocrystalline).
- 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 inclusions of iron oxides (goethite).
Quick Check
- Color: Golden-yellow to reddish-brown with chatoyancy.
- Luster: Silky to vitreous, chatoyant.
- Streak: White (due to quartz composition).
Physical Characteristics
- Crystal Habit: Massive, fibrous pseudomorphs after crocidolite.
- Cleavage Type: None.
- Fracture Type: Conchoidal to splintery.
- Tenacity: Brittle.
- Luster Type: Silky to vitreous, chatoyant.
Formation
Tiger's Eye forms as a pseudomorph of quartz after crocidolite (a fibrous amphibole mineral, specifically a type of asbestos). The process involves the replacement of the crocidolite fibers by chalcedony (cryptocrystalline quartz) while retaining the original fibrous structure. Iron oxides (primarily goethite) then infiltrate and stain the quartz, producing the characteristic golden-yellow to reddish-brown colors and the chatoyancy (cat's-eye effect). This replacement occurs under low-grade metamorphic conditions, often in serpentinite or other ultramafic rocks.
Usage
Primarily used as a gemstone for jewelry (cabochons, beads, carvings), ornamental objects, and decorative items. Its unique chatoyancy makes it highly prized. Historically, it was also believed to offer protection and good fortune.
Age Distribution
Typically found in Precambrian to Cenozoic age metamorphic rocks, with specific deposits varying in age.
Where to Find
Northern Cape Province, South Africa
The most significant and historically important deposits are found in the Griqualand West region, particularly around the towns of Prieska and Kuruman. These deposits are extensive and produce high-quality material.
Western Australia, Australia
Notable deposits occur in the Hamersley Range, particularly in the areas around Tom Price and Newman. These deposits also yield significant quantities of Tiger's Eye and Hawk's Eye.
Thailand
Smaller deposits are found in various regions, contributing to the global supply.
Myanmar (Burma)
Known for some occurrences, though less prominent than South Africa or Australia.
India
Limited occurrences have been reported.
United States (Arizona, California)
Minor occurrences have been found in certain states, but not on a commercial scale comparable to major producers.
Finding Tips
Look for Metamorphic Terrains
Tiger's Eye is typically found in low-grade metamorphic environments, often associated with serpentinite or other ultramafic rock formations. Geologic maps indicating such areas are a good starting point.
Identify Veins and Seams
It commonly occurs in veins or seams within the host rock. Look for linear features or bands of distinct color and texture within rock outcrops.
Observe Chatoyancy
The most distinctive feature is its chatoyancy. When examining potential specimens, rotate them under a light source to observe the characteristic moving band of light. This is crucial for identification.
Check for Fibrous Structure
While cryptocrystalline, a close examination of a broken surface or unpolished specimen may reveal a subtle fibrous texture, a remnant of the original crocidolite.
Consider Associated Minerals
Tiger's Eye can be found alongside other minerals typical of metamorphic environments, though its formation is quite specific. Look for iron-stained rocks.
Safety Warning: Crocidolite Origin
Tiger's Eye forms from the replacement of crocidolite, a type of asbestos. While the quartz replacement process generally renders the material safe by encapsulating or replacing the hazardous fibers, raw, unpolished specimens, especially those with incomplete silicification, may still contain residual crocidolite. Exercise caution when handling unpolished or raw Tiger's Eye, particularly if it appears unusually fibrous or dusty. Avoid grinding or cutting raw material without proper respiratory protection and ventilation to prevent inhalation of potentially harmful fibers. Polished Tiger's Eye is generally considered safe.
Similar Rocks
Hawk's Eye
Hawk's Eye (a variety of Chalcedony, which is a cryptocrystalline form of Quartz)
Also known as: Blue Tiger's Eye
Cat's Eye Chrysoberyl
Chrysoberyl var. Cymophane
Also known as: Cymophane
Pietersite
Pietersite (a brecciated chalcedony with embedded amphibole fibers)
Also known as: Tempest Stone
Scientific Classification
- Mineral Class
- Silicate (Tectosilicate)
- Group
- Quartz Group (Chalcedony variety)
- Crystal System
- Trigonal (cryptocrystalline)
- Chemical Formula
- SiO₂ (with FeO(OH) inclusions)
- Composition
- Silicon dioxide with fibrous inclusions of iron hydroxide (goethite) that replaced original crocidolite fibers.
Explore Tiger's Eye
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.