Tiger's Eye and Turquoise
Tiger's Eye (fibrous chalcedony, a variety of quartz) and Turquoise (hydrated phosphate of copper and aluminium)
Also known as: Tiger's Eye: Crocidolite Cat's Eye, African Cat's Eye; Turquoise: Callais, Turkish Stone
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, resembling the eye of a tiger. This optical effect is caused by the parallel intergrowth of quartz fibers and altered amphibole minerals. Its colors range from golden yellow to reddish-brown. Turquoise is an opaque, blue-to-green mineral, often found in nodular or botryoidal forms, or as vein fillings. Its color is due to copper (blue) and iron (green), and it often contains matrix inclusions of the host rock, such as limonite or sandstone.
How to Identify
- Color
- Tiger's Eye: Golden yellow, golden brown, reddish-brown, sometimes blue (Hawk's Eye). Turquoise: Sky blue, robin's egg blue, blue-green, apple green.
- Luster
- Tiger's Eye: Silky, vitreous. Turquoise: Waxy to subvitreous.
- Texture
- Tiger's Eye: Fibrous, often polished smooth. Turquoise: Cryptocrystalline, massive, often with a fine-grained texture.
- Crystal Form
- Tiger's Eye: Pseudomorph after fibrous crocidolite, typically massive or in veins. Turquoise: Cryptocrystalline, massive, reniform, botryoidal, stalactitic, or as veinlets.
- Cleavage
- Tiger's Eye: None (due to cryptocrystalline quartz). Turquoise: Perfect on {001}, but rarely observed due to cryptocrystalline nature.
- Geological Environment
- Tiger's Eye: Formed in metamorphosed iron formations, often associated with asbestos deposits. Turquoise: Secondary mineral in highly altered igneous (e.g., porphyry copper deposits) or metamorphic rocks, typically in arid or semi-arid regions, often in association with limonite, kaolinite, and other copper minerals.
Key Facts
- Hardness: Tiger's Eye: 6.5-7 on Mohs scale. Turquoise: 5-6 on Mohs scale.
- Specific Gravity: Tiger's Eye: 2.64-2.71. Turquoise: 2.60-2.90.
- Crystal System: Tiger's Eye: Trigonal (cryptocrystalline quartz). Turquoise: Triclinic.
- Color: Tiger's Eye: Golden yellow, golden brown, reddish-brown. Turquoise: Sky blue, robin's egg blue, blue-green, apple green.
- Luster: Tiger's Eye: Silky, vitreous. Turquoise: Waxy to subvitreous.
- Transparency: Tiger's Eye: Opaque to translucent. Turquoise: Opaque.
- Fracture: Tiger's Eye: Splintery to conchoidal. Turquoise: Conchoidal to uneven.
- Cleavage: Tiger's Eye: None. Turquoise: Perfect on {001}, but rarely observed.
- Composition: Tiger's Eye: Silicon dioxide (SiO2) with fibrous inclusions of limonite and altered crocidolite. Turquoise: Hydrated copper aluminum phosphate (CuAl6(PO4)4(OH)8·4H2O).
Quick Check
- Color: Tiger's Eye: Golden-brown, yellow, red-brown. Turquoise: Blue, blue-green, green.
- Luster: Tiger's Eye: Silky. Turquoise: Waxy to dull.
- Streak: Tiger's Eye: White. Turquoise: White to pale blue-green.
Physical Characteristics
- Crystal Habit: Tiger's Eye: Pseudomorph after fibrous crocidolite, massive. Turquoise: Cryptocrystalline, massive, reniform, botryoidal, stalactitic, veinlets.
- Cleavage Type: Tiger's Eye: None. Turquoise: Perfect on {001}, but typically not seen.
- Fracture Type: Tiger's Eye: Splintery to conchoidal. Turquoise: Conchoidal to uneven.
- Tenacity: Tiger's Eye: Brittle. Turquoise: Brittle.
- Luster Type: Tiger's Eye: Silky, vitreous. Turquoise: Waxy to subvitreous.
Formation
Tiger's Eye forms when quartz replaces crocidolite (a fibrous amphibole mineral) through a pseudomorphic process. The parallel fibers of crocidolite are replaced by quartz, and iron oxides (limonite) provide the golden-brown color and chatoyancy. Turquoise forms as a secondary mineral in arid regions, typically in aluminum-rich igneous or metamorphic rocks that have been altered by hydrothermal solutions. Copper, aluminum, and phosphorus-bearing waters percolate through fractures, depositing turquoise.
Usage
Both Tiger's Eye and Turquoise are primarily used as gemstones for jewelry, ornamental objects, and carvings. Tiger's Eye is valued for its chatoyancy, while Turquoise is prized for its unique blue-green color. Historically, Turquoise has been used in religious artifacts and as a protective amulet by various cultures.
Age Distribution
Tiger's Eye: Precambrian to Cenozoic; Turquoise: Varies, often associated with younger volcanic activity and arid environments.
Where to Find
Tiger's Eye: South Africa
The primary source of high-quality Tiger's Eye, particularly in the Griqualand West region.
Tiger's Eye: Australia
Significant deposits found in Western Australia.
Tiger's Eye: India, Myanmar, USA (California)
Other notable occurrences, though generally smaller in scale.
Turquoise: Southwestern United States (Arizona, Nevada, New Mexico, Colorado)
Historically and currently major producers of high-quality turquoise, often associated with copper mining districts.
Turquoise: Iran (Persia)
Renowned for its 'Persian blue' turquoise, considered among the finest in the world.
Turquoise: China (Hubei province)
A significant producer, with a wide range of colors and qualities.
Turquoise: Egypt (Sinai Peninsula)
Ancient mining sites, dating back thousands of years.
Turquoise: Mexico, Afghanistan, Australia, Chile
Other important sources of turquoise.
Finding Tips
Tiger's Eye: Look for Chatoyancy
When searching for Tiger's Eye, look for rocks that exhibit a silky, shimmering band of light that moves across the surface as the stone is rotated. This is its most distinctive feature.
Tiger's Eye: Associated Minerals
Tiger's Eye is often found in association with other quartz varieties and iron-rich metamorphic rocks. Look for areas with evidence of past asbestos mining (though exercise extreme caution due to health risks).
Turquoise: Arid Environments
Turquoise typically forms in arid or semi-arid regions. Focus your search in areas with altered igneous or metamorphic rocks, particularly those showing signs of copper mineralization (e.g., malachite, azurite stains).
Turquoise: Veins and Nodules
Turquoise often occurs as thin veinlets filling fractures or as small nodules within the host rock. Look for distinctive blue-green coloration against lighter rock matrices.
Turquoise: Matrix Inclusions
Many turquoise specimens contain remnants of the host rock, known as matrix. This can be black, brown, or yellowish and often forms attractive patterns (spiderweb matrix).
Safety Precaution: Tiger's Eye
Raw Tiger's Eye can sometimes contain remnants of crocidolite asbestos. While the quartz replacement process generally renders it safe, it is prudent to avoid inhaling dust from cutting or grinding unpolished specimens. Always wear appropriate respiratory protection when working with raw material.
Similar Rocks
Hawk's Eye
Fibrous Chalcedony (variety of Quartz)
Also known as: Blue Tiger's Eye
Cat's Eye Chrysoberyl
Chrysoberyl
Also known as: Cymophane
Variscite
Hydrated Aluminum Phosphate
Also known as: Utahlite
Chrysocolla
Hydrated Copper Silicate
Also known as: Gem Silica
Scientific Classification
- Mineral Class
- Tiger's Eye: Silicate (Tectosilicate, variety of Quartz). Turquoise: Phosphate.
- Group
- Tiger's Eye: Quartz Group. Turquoise: Turquoise Group.
- Crystal System
- Tiger's Eye: Trigonal. Turquoise: Triclinic.
- Chemical Formula
- Tiger's Eye: SiO2 (with inclusions). Turquoise: CuAl6(PO4)4(OH)8·4H2O
- Composition
- Tiger's Eye: Silicon dioxide with iron oxide and altered amphibole inclusions. Turquoise: Hydrated copper aluminum phosphate.
Explore Tiger's Eye and Turquoise
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.