sedimentary

Oyster Shell (Biogenic Calcium Carbonate)

Crassostrea virginica (or related species) - Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs scale); Color: Pearly white, grey, or cream with iridescent luster (nacre); Crystal Structure: Orthorhombic/Hexagonal (Aragonite/Calcite); Cleavage: None/Fragmentary; Specific Gravity: 2.7-2.9.

Hardness: 3-4 (Mohs scale)
Color: Pearly white, grey, or cream with iridescent luster (nacre)

Identified June 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Biogenic formation through accretion by marine mollusks. While shells can be modern, fossilized versions often date to the Cenozoic era. They form in marine or brackish estuarine environments as the organism extracts minerals from seawater.

Uses & applications

Used in decorative arts (mother-of-pearl), jewelry, construction (as aggregate or lime), soil conditioners in agriculture, and poultry feed supplements.

Geological facts

Shells are the primary source of 'coquina' stone, a type of sedimentary rock. They can survive for millions of years in the fossil record and provide vital data on ancient ocean temperatures and chemistry.

Field identification & locations

Identify by the presence of a distinct adductor muscle scar (the darker patch) and the layered, pearly interior. Commonly found on coastal shorelines, estuaries, and in fossiliferous limestone beds.

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