Black Freshwater Pearls

Physical Properties

Hardness: 2.5-4.5 (Mohs); Color: Peacock/Black with iridescent overtones; Luster: Pearly/Nacreous; Crystal structure: Orthorhombic aragonite platelets; Specific Gravity: 2.60-2.85

Formation & Geological History

Formed biogenically within the soft tissue (mantle) of living mollusks, typically freshwater mussels. Most modern black freshwater pearls are dyed or irradiated to achieve their dark color, as natural black freshwater pearls are extremely rare.

Uses & Applications

Primarily used in jewelry (necklaces, earrings, bracelets) and as decorative gemstones. Culturing pearls is a major global industry.

Geological Facts

Unlike minerals formed by geological pressure in the earth, pearls are organic gemstones. The 'orient' or rainbow-like surface shimmer is caused by the diffraction of light through successive layers of nacre.

Field Identification & Locations

Identify by the 'tooth test' (rubbing against teeth feels gritty, whereas plastic/glass is smooth) or by looking for drill holes for thread. Commonly cultured in lakes and rivers in China.

Identified on: 4/21/2026

Mode: Standard