mineral

Freshwater Pearl

Aragonite / Biogenic Calcium Carbonate (CaCO3)

Hardness: 2.5–4.5; Color: Cream, pink, lavender, or white with iridescence; Luster: Pearly (orient); Crystal structure: Orthorhombic (as aragonite platelets); Cleavage: None; Specific Gravity: 2.60–2.85

Hardness: 2
Color: Cream, pink, lavender, or white with iridescence
Luster: Pearly (orient)

Identified May 3, 2026More mineral →

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Physical properties

Formation & geological history

Formed biogenically within the soft tissue (mantle) of freshwater mussels. Unlike geological minerals formed by tectonics, these are created when an organism secretes nacre over a microscopic irritant.

Uses & applications

Primarily used in jewelry (necklaces, earrings, bracelets) and as organic gemstones for collectors.

Geological facts

Freshwater pearls are unique because a single mussel can produce up to 50 pearls at once, whereas saltwater oysters usually only produce one or two. La Peregrina is one of the world's most famous historical pearls.

Field identification & locations

Identify in the field by the 'tooth test' (rubbing across teeth feels gritty, whereas glass/plastic is smooth). Commonly sourced from lakes and rivers in China, Japan, and the United States (Mississippi River basin).

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