gemstone

Tahitian black pearl strand

Cultured pearl; aragonite (CaCO₃) nacre

AI-generated identification · may be incorrect

Organic gemstone rather than a rock; Mohs hardness about 2.5–4.5, with dark gray-to-black nacre and strong peacock, blue, or green orient. Pearls have concentric/lamellar nacre, pearly luster, and no crystal cleavage; specific gravity is about 2.60–2.85.

Identified August 17, 2026More gemstone →

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Physical properties

Formation & geological history

Cultured in black-lipped oysters (Pinctada margaritifera), chiefly in French Polynesia; nacre forms around an implanted bead or tissue nucleus over roughly 12–24 months. The nacre is geologically young and biologically produced.

Uses & applications

Used primarily in fine jewelry; value depends on luster, surface quality, roundness, size, color, and matching. They are not used for construction or industry.

Geological facts

The characteristic iridescence results from light interference in microscopic aragonite platelet layers. “Black” Tahitian pearls are usually naturally dark gray with overtones, not solid black.

Field identification & locations

Identify by smooth nacre, orient that shifts with angle, organic variation, and a gritty feel when two pearls are gently rubbed; imitation glass or plastic lacks this structure. Commonly associated with French Polynesia, the Cook Islands, and other tropical Pacific farms.