mineral

Atlantic Calico Scallop (Biogenic Aragonite/Calcite)

Argopecten gibbus (Chemical: CaCO3)

Hardness: 3-3.5 (Mohs); Color: Mottled red, purple, and brown patterns on a white base; Luster: Pearly to dull; Structure: Fan-shaped bivalve with 19-22 radiating ribs; Cleavage: None (conchoidal fracture).

Hardness: 3-3
Color: Mottled red, purple, and brown patterns on a white base
Luster: Pearly to dull

Identified March 22, 2026More mineral →

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Physical properties

Formation & geological history

Biogenic formation by marine mollusks; shells consist of secreted calcium carbonate layers. Living specimens date to the Holocene, but fossilized versions are found in Pliocene and Pleistocene sediment layers (approx. 2-5 million years old).

Uses & applications

Used in the seafood industry, for decorative arts, jewelry making, aquarium substrate, and as a source of lime in soil conditioners.

Geological facts

Unlike most bivalves, scallops can swim by rapidly opening and closing their shells to expel water. They also have dozens of tiny blue eyes along the edge of their mantle to detect motion.

Field identification & locations

Identify in the field by its distinct 'ears' (auricles) at the hinge and mottled 'calico' pattern. Commonly found along the Atlantic coast from North Carolina to Brazil, especially on Florida beaches.

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