fossil

Oyster shell fragment

Ostreidae shell; primarily calcite (CaCO₃)

AI-generated identification · may be incorrect

Hardness about 3 Mohs; cream, tan, and gray, with a pearly to dull luster, layered fibrous structure, irregular ribs, and no true cleavage. The thick, curved form and porous interior are typical of a bivalve shell rather than a crystalline rock.

Identified August 9, 2026More fossil →

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Physical properties

Formation & geological history

A biological carbonate shell formed by an oyster in a marine environment; it may be modern or subfossil, but the image alone cannot establish its age. Burial and mineral alteration can preserve or partially recrystallize the calcite.

Uses & applications

Used for lime and cement, soil amendment, poultry feed calcium, aggregate, and decorative crafts; intact shells are collected more than fragments. This piece has minimal commercial value.

Geological facts

Oyster shells consist of calcite layers secreted by the animal and commonly show a smooth inner nacreous surface with a rougher outer surface. Vinegar or dilute hydrochloric acid causes visible fizzing because of the carbonate.

Field identification & locations

Identify it by its curved bivalve shape, layered shell texture, chalky porous break, and acid reaction; it is commonly found on beaches, oyster beds, and shell middens worldwide. It is not a conventional igneous, sedimentary, or metamorphic rock.