sedimentary

Oyster Shell (Aragonite/Calcite)

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs Scale), Color: Pearly white to off-white, Luster: Nacreous/shirry interior with dull exterior, Crystal structure: Orthorhombic (Aragonite) or Trigonal (Calcite), Cleavage: Perfect in minerals, but conchoidal in shell structure, Specific gravity: 2.7–2.9

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Biogenic formation by marine mollusks; shells accumulate in marine environments and can eventually lithify into limestone or coquina over millions of years. This specific specimen appears modern or sub-fossilized.

Uses & applications

Used in the production of lime (industrial), road aggregate, chicken feed calcium supplement, and decorative artisan crafts. Historically used in buttons and early 'Mother-of-Pearl' items.

Geological facts

Oyster shells are biomineralized structures. The inner iridescent layer is known as nacre. They are essential to ocean health as they form reefs that provide habitat for other species and filter pollutants from water.

Field identification & locations

Identify by the distinctive cupped shape or hinge line. Frequently found on beaches or in coastal sediment deposits. For collectors, search for 'fossilized' shells which may have replaced minerals like chalcedony or pyrite.

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