How to identify Tiger's Eye
Quartz (fibrous crocidolite)
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Open the appTo correctly identify Tiger's Eye (Quartz (fibrous crocidolite)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.
Step-by-step identification
- 1
Color
Overall color and any zoning or banding
Golden-yellow, golden-brown, reddish-brown, sometimes blue (Hawk's Eye). The color is due to iron oxides.
- 2
Luster
How the surface reflects light: metallic, vitreous, dull
Silky to vitreous, exhibiting strong chatoyancy.
- 3
Texture
Grain size and surface feel: coarse, fine, glassy
Fibrous, often with a fine-grained, compact appearance. When polished, it feels smooth.
- 4
Crystal Form
Shape of visible crystals or crystal faces
Massive, fibrous aggregates. Does not form macroscopic crystals of its own, as it is a pseudomorph.
- 5
Cleavage
How it breaks: flat cleavage planes vs irregular fracture
None, due to its microcrystalline quartz nature. The fibrous structure of the original crocidolite is preserved but not true cleavage.
- 6
Geological Environment
The rock formation and setting where it occurs
Typically found in metamorphosed banded iron formations (BIFs) or other iron-rich sedimentary rocks that have undergone low-grade regional metamorphism. It forms in veins or layers within these host rocks.
Key Facts
- Hardness
- 7 (Mohs scale)
- Specific Gravity
- 2.64 - 2.71
- Crystal System
- Trigonal (as quartz)
- Color
- Golden-yellow, golden-brown, reddish-brown, blue (Hawk's Eye)
- Luster
- Silky to vitreous, chatoyant
- Transparency
- Opaque to translucent
- Fracture
- Conchoidal to splintery (due to fibrous structure)
- Cleavage
- None
- Composition
- Silicon dioxide (SiO2) with fibrous inclusions of altered crocidolite and iron oxides.
Physical characteristics
- Crystal Habit: Massive, fibrous aggregates, pseudomorph after crocidolite.
- Cleavage Type: None
- Fracture Type: Conchoidal to splintery
- Tenacity: Brittle
- Luster Type: Silky, chatoyant
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