mineraloid
Black Pearl (Tahitian Type)
Aragonite / Conchiolin composite (CaCO3)
Hardness: 2.5–4.5; Color: Dark grey, peacock green, blue, or black with iridescence; Luster: Pearly (pearly-metallic); Structure: Orthorhombic microcrystals; Specific Gravity: 2.60–2.85.
- Hardness
- 2
- Color
- Dark grey, peacock green, blue, or black with iridescence
- Luster
- Pearly (pearly-metallic)
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Physical properties
Hardness: 2.5–4.5; Color: Dark grey, peacock green, blue, or black with iridescence; Luster: Pearly (pearly-metallic); Structure: Orthorhombic microcrystals; Specific Gravity: 2.60–2.85.
Formation & geological history
Formed biogenically within the soft tissue (mantle) of a living shelled mollusk, specifically the Pinctada margaritifera. It is a defense mechanism where layers of nacre are deposited around an irritant.
Uses & applications
Primary use is in fine jewelry (rings, necklaces, earrings). Highly valued for aesthetic beauty and as a status symbol.
Geological facts
Black pearls are often called 'Tahitian Pearls,' though they can come from various islands in French Polynesia. They are the only pearls with a naturally occurring dark color.
Field identification & locations
Identify by checking for 'overtone' (a secondary color shimmying over the surface) and the 'tooth test' (feels gritty against teeth, unlike smooth plastic fakes). Found in warm tropical lagoons.
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