Pearl

Physical Properties

Hardness: 2.5–4.5 (Mohs scale); Color: White, cream, pink, or silver; Luster: Pearly (iridescent); Crystal structure: Orthorhombic (as aragonite platelets); Cleavage: None; Specific gravity: 2.60–2.85.

Formation & Geological History

Formed biogenically within the soft tissue (mantle) of living shelled mollusks (oysters or mussels). It consists of calcium carbonate deposited in concentric layers. While not 'geological age' in the traditional sense, they are modern biogenic minerals.

Uses & Applications

Primarily used in high-end jewelry (necklaces, earrings, rings) and as a traditional gemstone. Historically used in cosmetics and medicines in powdered form.

Geological Facts

Pearls are the only gemstones made by living animals. The pearl's unique iridescence (orient) is caused by the interference and diffraction of light on the microscopic layers of aragonite.

Field Identification & Locations

Field identification: The 'tooth test' (rubbing against teeth feels gritty, whereas fakes feel smooth). Identified by luster and weight. Found in saltwater (oceans) and freshwater (rivers/lakes) inside host mollusks.

Identified on: 4/25/2026

Mode: Standard