How to identify Tiger's Eye, Pearl, and Onyx

To correctly identify Tiger's Eye, Pearl, and Onyx (Quartz (Tiger's Eye), Calcium Carbonate (Pearl), Chalcedony (Onyx)), 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

   Tiger's Eye: Golden to red-brown with chatoyant bands. Pearl: White, cream, pink, silver, black, blue, green, yellow, purple. Onyx: Typically black, or black and white banded (sardonyx is red-brown and white).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Tiger's Eye: Silky, chatoyant. Pearl: Pearly (nacreous). Onyx: Waxy to vitreous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Tiger's Eye: Fibrous appearance due to chatoyancy. Pearl: Smooth, sometimes slightly textured due to nacre layers. Onyx: Smooth, microcrystalline.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Tiger's Eye: Pseudomorph after fibrous crocidolite, massive. Pearl: Concentric layers of nacre, typically spherical or irregular. Onyx: Cryptocrystalline, massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Tiger's Eye: None (quartz). Pearl: None. Onyx: None (chalcedony).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Tiger's Eye: Formed in highly metamorphosed iron formations. Pearl: Marine or freshwater mollusk shells. Onyx: Hydrothermal veins, volcanic gas cavities, or sedimentary deposits.

Key Facts

Hardness

Tiger's Eye: 6.5-7 (Mohs). Pearl: 2.5-4.5 (Mohs). Onyx: 6.5-7 (Mohs).

Specific Gravity

Tiger's Eye: 2.64-2.71. Pearl: 2.60-2.85. Onyx: 2.58-2.64.

Crystal System

Tiger's Eye: Trigonal (quartz). Pearl: Orthorhombic (aragonite) or Trigonal (calcite). Onyx: Trigonal (chalcedony, microcrystalline quartz).

Color

Tiger's Eye: Golden-yellow to red-brown. Pearl: White, cream, pink, black, various body colors with overtone. Onyx: Black, white, brown, often banded.

Luster

Tiger's Eye: Silky, chatoyant. Pearl: Pearly (nacreous). Onyx: Waxy to vitreous.

Transparency

Tiger's Eye: Opaque to translucent. Pearl: Opaque. Onyx: Opaque to translucent.

Fracture

Tiger's Eye: Conchoidal. Pearl: Uneven. Onyx: Conchoidal to uneven.

Cleavage

Tiger's Eye: None. Pearl: None. Onyx: None.

Composition

Tiger's Eye: Silicon dioxide (SiO2) with fibrous inclusions of altered crocidolite. Pearl: Calcium carbonate (CaCO3) in the form of aragonite or calcite, with conchiolin. Onyx: Silicon dioxide (SiO2).

Physical characteristics

• Crystal Habit: Tiger's Eye: Pseudomorphous after fibrous amphibole, massive. Pearl: Concentric layers, typically spherical, baroque, or button-shaped. Onyx: Cryptocrystalline, massive.
• Cleavage Type: Tiger's Eye: None. Pearl: None. Onyx: None.
• Fracture Type: Tiger's Eye: Conchoidal. Pearl: Uneven. Onyx: Conchoidal to uneven.
• Tenacity: Tiger's Eye: Brittle. Pearl: Tough. Onyx: Tough.
• Luster Type: Tiger's Eye: Silky. Pearl: Pearly. Onyx: Waxy to vitreous.

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