Mineral (Organic)

Natural or Cultured Pearl

Calcium Carbonate (Aragonite and Conchiolin), CaCO3

Hardness: 2.5-4.5 (Mohs scale); Color: Cream, white, or yellowish; Luster: Pearly (iridescent); Crystal structure: Orthorhombic (microcrystalline); Cleavage: None; Specific gravity: 2.60-2.85.

Hardness: 2
Color: Cream, white, or yellowish
Luster: Pearly (iridescent)

Identified March 11, 2026More mineral (organic) →

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Physical properties

Hardness: 2.5-4.5 (Mohs scale); Color: Cream, white, or yellowish; Luster: Pearly (iridescent); Crystal structure: Orthorhombic (microcrystalline); Cleavage: None; Specific gravity: 2.60-2.85.

Formation & geological history

Formed within the soft tissue of a living shelled mollusk. Layers of nacre are deposited around an irritant such as a parasite or a piece of organic material. Natural pearls are rare, while most modern pearls are cultured in pearl farms.

Uses & applications

Primarily used in jewelry (necklaces, earrings, rings) and as a birthstone. Historically used in ornate decorations and sometimes ground for traditional medicines or cosmetics.

Geological facts

Pearls are the only gemstones made by living creatures. The 'tooth test' (rubbing the pearl against the edge of a tooth) can identify real pearls by their gritty texture compared to smooth glass or plastic imitations.

Field identification & locations

Identify by inspecting the surface for a slight luster (orient) and checking for a nacreous texture. They are found in both marine and freshwater environments where host oysters, mussels, or clams reside.

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Precious Red Coral

Corallium rubrum (Calcium Carbonate, CaCO3)

Mineral (Organic Gemstone)

Precious Red Coral

Corallium rubrum / Corallium japonicum

mineral (organic gemstone)

Coral (Precious Coral)

Corallium rubrum (Red Coral), Paracorallium japonicum (Momo Coral), Pleurocorallium elatius (Sardinian Coral), various other species within the Corallidae family. Chemically, it's primarily Calcium Carbonate (CaCO 3 ).

Mineral, Organic Gemstone

Banded Chert / Banded Jasper (likely a variety of Chert/Chalcedony)

Chert (microcrystalline quartz)

Metamorphic Rock

Amber

Succinite (formula varies, primarily C10H16O)

Mineraloid (Organic)

Amber

Succinicum (C10H16O)

mineral