Pearl (Biogenic Mineraloid)

Physical Properties

Hardness: 2.5-4.5 (Mohs scale); Color: Creamy white with iridescent orient; Luster: Pearly; Crystal structure: Orthorhombic (Aragonite plates); Cleavage: None; Specific Gravity: 2.60-2.85

Formation & Geological History

Formed within the soft tissue (mantle) of living shelled mollusks, such as oysters and mussels. It is a biogenic process where thin layers of nacre are deposited around an irritant.

Uses & Applications

Primarily used in jewelry (necklaces, earrings, rings), ornamentation, and historically in cosmetics or medicine (pearl powder).

Geological Facts

Pearls are the only gemstones created by living creatures. Unlike traditional minerals formed deep in the earth, pearls are made of organic conchiolin and inorganic aragonite. The specimen in the image appears to be freshwater cultured pearls, indicated by their slightly irregular 'potato' or baroque shapes.

Field Identification & Locations

Identify by the 'tooth test' (pearls feel gritty against teeth, imitations feel smooth), presence of surface concentric growth rings (as seen in the image), and iridescent luster. Commonly found in pearl farms in China, Japan, and the South Pacific.

Identified on: 4/21/2026

Mode: Standard