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This combination refers to three distinct materials, each with unique geological origins and compositions. Tiger's Eye is a chatoyant gemstone, typically golden to red-brown, exhibiting a silky luster due to parallel intergrowth of quartz and altered amphibole fibers. Pearl is an organic gem, iridescent and typically white, cream, or black, formed by layers of nacre. Onyx is a banded variety of chalcedony, often black and white, or entirely black, known for its fine grain and ability to take a high polish.
How to Identify
- Color
- 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).
- Luster
- Tiger's Eye: Silky, chatoyant. Pearl: Pearly (nacreous). Onyx: Waxy to vitreous.
- Texture
- Tiger's Eye: Fibrous appearance due to chatoyancy. Pearl: Smooth, sometimes slightly textured due to nacre layers. Onyx: Smooth, microcrystalline.
- Crystal Form
- Tiger's Eye: Pseudomorph after fibrous crocidolite, massive. Pearl: Concentric layers of nacre, typically spherical or irregular. Onyx: Cryptocrystalline, massive.
- Cleavage
- Tiger's Eye: None (quartz). Pearl: None. Onyx: None (chalcedony).
- Geological Environment
- 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).
Quick Check
- Color: Tiger's Eye: Golden-brown, red-brown. Pearl: White, cream, black, various iridescent hues. Onyx: Black, or black and white banded.
- Luster: Tiger's Eye: Silky, chatoyant. Pearl: Pearly. Onyx: Waxy to vitreous.
- Streak: Tiger's Eye: White. Pearl: White. Onyx: White.
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.
Formation
Tiger's Eye: Formed by the alteration of crocidolite (asbestos) within quartz, where fibrous amphibole minerals are replaced by silica while retaining their fibrous structure. Pearl: Formed within the soft tissue (mantle) of a living shelled mollusk or another animal, as a defense mechanism against an irritant. Onyx: A cryptocrystalline variety of quartz, typically formed in the gas cavities of volcanic rocks or as a banded sedimentary deposit.
Usage
All three are widely used in jewelry, ornamental objects, and decorative carvings. Tiger's Eye is also used in lapidary arts. Pearl is a classic gemstone. Onyx is used for cameos, intaglios, and architectural decoration.
Age Distribution
Tiger's Eye: Precambrian to Cenozoic; Pearl: Holocene (modern to recent); Onyx: Precambrian to Cenozoic
Where to Find
Tiger's Eye
Major deposits are found in South Africa (Griqualand West), Australia (Pilbara region), India, Myanmar, Namibia, and the USA (California).
Pearl
Natural pearls are found in various marine and freshwater environments globally, with historical significance in the Persian Gulf, Red Sea, and waters around Japan, Australia, and the Philippines. Cultured pearls are produced worldwide, notably in Japan, China, Australia, and French Polynesia.
Onyx
Significant occurrences include Brazil, Uruguay, India, Madagascar, Mexico, Pakistan, and the USA (Arizona, California).
Finding Tips
Tiger's Eye Identification
Look for the characteristic chatoyancy (cat's eye effect) and golden-brown to reddish-brown color. It often occurs in banded iron formations.
Pearl Identification
Natural pearls are rare. Look for iridescence (orient), smooth surface, and a slightly gritty feel when rubbed against a tooth (for natural/cultured pearls, not imitations). Consider the environment: marine or freshwater mollusk habitats.
Onyx Identification
Identify by its fine-grained, cryptocrystalline texture and characteristic banding (often black and white) or uniform black color. It can be found in volcanic areas or sedimentary layers.
Safety for Tiger's Eye
While the crocidolite (asbestos) in Tiger's Eye is fully silicified and therefore not friable or hazardous in its finished form, raw or unpolished specimens, especially those showing blue crocidolite (Hawk's Eye), should be handled with care to avoid inhaling any potential dust if broken or abraded. Always wear appropriate respiratory protection when cutting or polishing any silica-bearing material.
Similar Rocks
Hawk's Eye
Quartz (with crocidolite)
Also known as: Blue Tiger's Eye
Cat's Eye Chrysoberyl
Chrysoberyl
Also known as: Cymophane
Mother-of-Pearl
Calcium Carbonate (aragonite)
Also known as: Nacre
Agate
Chalcedony (microcrystalline quartz)
Also known as: Banded Chalcedony
Jasper
Chalcedony (microcrystalline quartz)
Also known as: Opaque Chalcedony
Scientific Classification
- Mineral Class
- Tiger's Eye: Silicate (Tectosilicate). Pearl: Carbonate. Onyx: Silicate (Tectosilicate).
- Group
- Tiger's Eye: Quartz Group. Pearl: Aragonite/Calcite. Onyx: Chalcedony (Quartz Group).
- Crystal System
- Tiger's Eye: Trigonal. Pearl: Orthorhombic (aragonite) or Trigonal (calcite). Onyx: Trigonal.
- Chemical Formula
- Tiger's Eye: SiO2 (with FeO(OH) inclusions). Pearl: CaCO3 + conchiolin + H2O. Onyx: SiO2.
- Composition
- Tiger's Eye: Silicon dioxide with iron hydroxide inclusions. Pearl: Calcium carbonate (aragonite/calcite) and organic binder (conchiolin). Onyx: Microcrystalline quartz.
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