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Red Tiger's Eye is a captivating variety of Tiger's Eye, characterized by its rich reddish-brown to brick-red color and prominent chatoyancy (a silky, luminous streak of light that moves across the surface as the stone is rotated). This optical effect, often referred to as the 'cat's eye' effect, is caused by the reflection of light from parallel fibrous inclusions within the quartz. The red coloration distinguishes it from the more common golden-brown Tiger's Eye and is a result of higher iron oxidation.
How to Identify
- Color
- Deep reddish-brown to brick-red, often with streaks of darker or lighter red. The color is uniform throughout the chatoyant bands.
- Luster
- Silky to vitreous, especially on polished surfaces, with a distinct chatoyancy.
- Texture
- Fine-grained, fibrous appearance internally, though externally smooth when polished. Can feel cool and dense.
- Crystal Form
- Massive, cryptocrystalline aggregates, typically forming veins or layers. Does not exhibit macroscopic crystal faces.
- Cleavage
- None, due to its cryptocrystalline nature.
- Geological Environment
- Found in metamorphosed banded iron formations or other environments where crocidolite asbestos has been altered by silica-rich hydrothermal fluids or metasomatism. Often associated with serpentinites and other metamorphic rocks.
Key Facts
- Hardness: 6.5-7 on the Mohs scale (due to quartz composition).
- Specific Gravity: 2.64-2.71 g/cm³.
- Crystal System: Trigonal (as quartz).
- Color: Reddish-brown, brick-red, often with golden or darker streaks.
- 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 (hematite, goethite) that replaced crocidolite.
Quick Check
- Color: Reddish-brown to brick-red with chatoyant bands.
- Luster: Silky to vitreous.
- Streak: White.
Physical Characteristics
- Crystal Habit: Massive, cryptocrystalline, pseudomorph after fibrous crocidolite.
- Cleavage Type: None.
- Fracture Type: Conchoidal to splintery, due to its microcrystalline nature and fibrous structure.
- Tenacity: Brittle.
- Luster Type: Silky (due to fibrous inclusions) to vitreous (of the quartz matrix).
Formation
Red Tiger's Eye is a pseudomorph of quartz after crocidolite (a fibrous amphibole mineral, specifically riebeckite). The original formation involves the alteration of crocidolite asbestos by silicification, where quartz replaces the crocidolite fibers while retaining their fibrous structure. The red color is primarily due to further oxidation of iron within the quartz matrix, often through natural heating processes (e.g., metamorphism, hydrothermal activity) or sometimes through artificial heat treatment.
Usage
Primarily used as an ornamental stone, for cabochons, beads, carvings, and other lapidary applications. Its chatoyancy and attractive color make it popular in jewelry. It is also collected as a mineral specimen.
Age Distribution
Typically Precambrian to Phanerozoic, depending on the host rock formation.
Where to Find
South Africa
The primary source of high-quality Tiger's Eye, including Red Tiger's Eye, particularly in the Griqualand West region, Northern Cape Province. Occurs in extensive banded iron formations.
Australia
Western Australia, particularly the Hamersley Range, is another significant source, often found in similar geological settings to South Africa.
India
Some occurrences have been reported, though generally less prominent than South African or Australian deposits.
Myanmar (Burma)
Minor occurrences have been noted.
United States
Limited occurrences in states like Arizona and California, often associated with asbestos deposits.
Finding Tips
Look for Banded Iron Formations
Red Tiger's Eye is typically found in or near ancient banded iron formations (BIFs) where crocidolite asbestos was present. These are often found in Precambrian shield areas.
Identify Fibrous Structures
Even in its silicified form, the fibrous nature of the original crocidolite is preserved. Look for parallel, silky fibers within the rock.
Observe Chatoyancy
The most distinctive feature is its chatoyancy. Rotate potential specimens under a light source to observe the moving band of light.
Check for Reddish Hues
While some Red Tiger's Eye is naturally occurring, some is heat-treated. Natural Red Tiger's Eye will have a more consistent, often deeper, reddish-brown color compared to some artificially heated material which might show more orange or uneven coloration.
Safety Precautions
When collecting in areas known for crocidolite (asbestos) deposits, exercise extreme caution. While Red Tiger's Eye itself is silicified and generally safe, disturbing the surrounding rock could expose you to hazardous asbestos fibers. Always wear appropriate respiratory protection (P100 respirator) and avoid dry cutting or grinding in the field. Consult local geological surveys for safety guidelines.
Similar Rocks
Tiger's Eye
Quartz (variety of Tiger's Eye)
Also known as: African Tiger's Eye, Gold Tiger's Eye
Hawk's Eye
Quartz (variety of Tiger's Eye)
Also known as: Blue Tiger's Eye
Pietersite
Chalcedony with embedded amphibole fibers
Also known as: Tempest Stone
Scientific Classification
- Mineral Class
- Silicates (Tectosilicates)
- Group
- Quartz Group
- Crystal System
- Trigonal
- Chemical Formula
- SiO₂ (with iron oxide inclusions)
- Composition
- Silicon dioxide, with iron oxides (primarily hematite and goethite) responsible for the color and fibrous structure inherited from altered crocidolite.
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