How to identify Tiger's Eye

To correctly identify Tiger's Eye (Fibrous Crocidolite (a variety of Quartz)), 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. 1

   Color

   Overall color and any zoning or banding

   Golden-yellow, golden-brown, reddish-brown, sometimes blue (Hawk's Eye). The colors are typically banded or streaky.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to vitreous, with a distinct chatoyancy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fibrous, often with a fine-grained, compact appearance. Polished surfaces are smooth.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, fibrous aggregates, pseudomorphs after crocidolite. Individual crystals are microscopic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its quartz composition, but the fibrous structure can create a 'false cleavage' or parting along the fiber direction.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in metamorphosed banded iron formations, where crocidolite asbestos has been altered by silica-rich hydrothermal fluids.

Key Facts

Hardness

6.5-7 on the Mohs scale (due to quartz composition)

Specific Gravity

2.64-2.71

Crystal System

Trigonal (for quartz), but pseudomorphs retain the monoclinic fibrous habit of crocidolite

Color

Golden-yellow, golden-brown, reddish-brown, blue

Luster

Silky, vitreous

Transparency

Opaque to translucent

Fracture

Conchoidal to splintery (along fiber direction)

Cleavage

None (quartz), but a parting along the fibrous structure

Composition

Silicon dioxide (SiO2) with inclusions of iron oxides (goethite) and relict fibrous structure of crocidolite

Physical characteristics

• Crystal Habit: Massive, fibrous aggregates, pseudomorphs after crocidolite
• Cleavage Type: None (quartz), but a distinct parting along the fibrous structure
• Fracture Type: Conchoidal to splintery
• Tenacity: Brittle
• Luster Type: Silky to vitreous, with chatoyancy

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