How to identify Tiger's Eye

To correctly identify Tiger's Eye (Tiger's Eye (variety of Chalcedony, SiO2)), 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 with darker brown or black bands. The color is due to iron oxides.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to vitreous, exhibiting a distinct chatoyancy (a mobile, shimmering band of light).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained, fibrous appearance due to the pseudomorphic replacement of crocidolite. Smooth when polished.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Massive, fibrous aggregates. Does not form macroscopic crystals of its own, but rather preserves the fibrous habit of the original crocidolite.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its cryptocrystalline nature. Exhibits conchoidal to splintery fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in metamorphic rocks, particularly those rich in iron and silica, where crocidolite has undergone silicification. Often occurs in veins or seams within serpentinites or other mafic/ultramafic rocks.

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

2.64-2.71

Crystal System

Trigonal (as chalcedony, but pseudomorphs fibrous monoclinic crocidolite)

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 fibrous inclusions of iron oxides (goethite) and remnants of crocidolite.

Physical characteristics

• Crystal Habit: Massive, fibrous aggregates, pseudomorphing the original crocidolite fibers.
• Cleavage Type: None
• Fracture Type: Conchoidal to splintery
• Tenacity: Brittle
• Luster Type: Silky, chatoyant

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