Rock Identifier
Seashell (Cockle Shell) (Cardiidae (Bivalvia), primary composition: Calcium Carbonate (CaCO3) in the form of aragonite or calcite) — fossil
fossil

Seashell (Cockle Shell)

Cardiidae (Bivalvia), primary composition: Calcium Carbonate (CaCO3) in the form of aragonite or calcite

Hardness: 3-3.5 (Mohs scale); Color: Creamy white with brown/tan banding; Luster: Dull to pearly; Structure: Ribbed fan shape with prominent radial costae; Cleavage: None

Hardness
3-3
Color
Creamy white with brown/tan banding
Luster
Dull to pearly
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Physical properties

Hardness: 3-3.5 (Mohs scale); Color: Creamy white with brown/tan banding; Luster: Dull to pearly; Structure: Ribbed fan shape with prominent radial costae; Cleavage: None

Formation & geological history

Biogenic formation through accretion by marine mollusks; while this specimen is a modern biological remain, shells are the precursors to many sedimentary rock formations like limestone or coquina.

Uses & applications

Decorative use, jewelry, source of lime in construction, and educational collecting.

Geological facts

Cockles are heart-shaped when viewed from the side and can jump by using their foot. They are significant contributors to the formation of calcium carbonate deposits on the ocean floor.

Field identification & locations

Found on sandy beaches worldwide, especially during low tide. Identified by the symmetrical valves and strong radial ribs that interlock at the margins.

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