mineral

Pearl (Biogenic)

Nacre / Calcium Carbonate (CaCO3)

Hardness: 2.5-4.5 (Mohs); Color: White, cream, silver, or blue (shown); Luster: Pearly (iridescent); Crystal Structure: Orthorhombic (Aragonite); Specific Gravity: 2.60-2.85

Hardness: 2
Color: White, cream, silver, or blue (shown)
Luster: Pearly (iridescent)

Identified March 20, 2026More mineral →

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Physical properties

Hardness: 2.5-4.5 (Mohs); Color: White, cream, silver, or blue (shown); Luster: Pearly (iridescent); Crystal Structure: Orthorhombic (Aragonite); Specific Gravity: 2.60-2.85

Formation & geological history

Formed biogenically by mollusks (oysters, mussels) as a defense mechanism against irritants; layers of nacre are deposited over time. Can be natural or cultured in saltwater or freshwater.

Uses & applications

Primarily used in jewelry making, fine fashion accessories, and cosmetics (as pearl powder). High-grade specimens are highly valued in the gemstone market.

Geological facts

Pearls are the only gemstones made by a living creature. Unlike other gems, they require no cutting or polishing to reveal their natural beauty. The world's largest pearl, 'Pearl of Lao Tzu', weighs over 14 lbs.

Field identification & locations

Identify by the 'tooth test' (gritty feel against teeth) or by checking for concentric growth rings under magnification. Commonly found in tropical and subtropical ocean waters or freshwater lakes for cultured varieties.