How to identify Turquoise and Tiger's Eye

To correctly identify Turquoise and Tiger's Eye (Turquoise (CuAl6(PO4)4(OH)8·4H2O) and Tiger's Eye (fibrous crocidolite replaced by chalcedony)), 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

   Turquoise: Sky blue, blue-green, apple green. Tiger's Eye: Golden yellow, golden brown, reddish-brown, sometimes blue (Hawk's Eye).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Turquoise: Waxy to subvitreous. Tiger's Eye: Silky, chatoyant.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Turquoise: Cryptocrystalline, massive, reniform, botryoidal. Tiger's Eye: Fibrous, compact.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Turquoise: Rarely forms distinct crystals; typically massive, nodular, or as vein fillings. Tiger's Eye: Pseudomorph after fibrous crocidolite, maintaining the original fibrous structure.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Turquoise: Perfect on {001} (rarely observed due to cryptocrystalline nature). Tiger's Eye: None (due to fibrous quartz replacement).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Turquoise: Secondary mineral in arid regions, often in altered volcanic or sedimentary rocks rich in aluminum, with copper mineralization. Tiger's Eye: Formed in metamorphic rocks, specifically in banded iron formations where crocidolite asbestos has been altered.

Key Facts

Hardness

Turquoise: 5-6 on Mohs scale. Tiger's Eye: 6.5-7 on Mohs scale.

Specific Gravity

Turquoise: 2.60-2.90. Tiger's Eye: 2.64-2.71.

Crystal System

Turquoise: Triclinic. Tiger's Eye: Trigonal (as quartz pseudomorph).

Color

Turquoise: Blue, blue-green, green. Tiger's Eye: Golden-yellow, golden-brown, reddish-brown, blue (Hawk's Eye).

Luster

Turquoise: Waxy, subvitreous, dull. Tiger's Eye: Silky, chatoyant.

Transparency

Turquoise: Opaque. Tiger's Eye: Opaque.

Fracture

Turquoise: Conchoidal to uneven. Tiger's Eye: Splintery to conchoidal.

Cleavage

Turquoise: Perfect on {001} (rarely observed). Tiger's Eye: None.

Composition

Turquoise: Hydrous copper aluminum phosphate. Tiger's Eye: Silicon dioxide (SiO2) with fibrous inclusions of iron oxides.

Physical characteristics

• Crystal Habit: Turquoise: Massive, cryptocrystalline, reniform, botryoidal, stalactitic, encrusting. Tiger's Eye: Fibrous aggregates, pseudomorphs after crocidolite.
• Cleavage Type: Turquoise: Perfect on {001} (rarely seen). Tiger's Eye: None.
• Fracture Type: Turquoise: Conchoidal to uneven. Tiger's Eye: Splintery to conchoidal.
• Tenacity: Turquoise: Brittle. Tiger's Eye: Brittle.
• Luster Type: Turquoise: Waxy, subvitreous, dull. Tiger's Eye: Silky, chatoyant.

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