How to identify Tiger's Eye

To correctly identify Tiger's Eye (Tiger's Eye (variety of Chalcedony, a cryptocrystalline 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 with darker brown or black bands. The color is due to iron oxide inclusions.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Silky to vitreous, exhibiting a distinct chatoyancy (cat's-eye effect) when polished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Fine-grained, fibrous appearance internally, though cryptocrystalline. Smooth when polished.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically massive, occurring in veins or layers. Does not form macroscopic crystals, but rather microscopic fibrous aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, due to its cryptocrystalline nature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in metamorphosed iron-rich rocks, often associated with crocidolite deposits. It forms in veins or layers within these host rocks, where hydrothermal fluids facilitate the pseudomorphic replacement process.

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

2.64-2.71

Crystal System

Trigonal (as quartz, but cryptocrystalline aggregates)

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 inclusions of iron oxides (goethite) and relict amphibole fibers.

Physical characteristics

• Crystal Habit: Massive, fibrous aggregates, pseudomorph after crocidolite.
• Cleavage Type: None
• Fracture Type: Conchoidal to splintery
• Tenacity: Brittle
• Luster Type: Silky (due to chatoyancy) to vitreous

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