sedimentary
Bay Scallop Shell
Argopecten irradians (Biogenic Calcium Carbonate / CaCO3)
Hardness: 3-3.5 (Mohs scale); Color: Variegated grays, browns, and whites with dark banding; Luster: Dull to pearly (nacreous interior); Crystal Structure: Orthorhombic (as aragonite) or Trigonal (as calcite); Cleavage: None (conchoidal fracture).
- Hardness
- 3-3
- Color
- Variegated grays, browns, and whites with dark banding
- Luster
- Dull to pearly (nacreous interior)
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Physical properties
Hardness: 3-3.5 (Mohs scale); Color: Variegated grays, browns, and whites with dark banding; Luster: Dull to pearly (nacreous interior); Crystal Structure: Orthorhombic (as aragonite) or Trigonal (as calcite); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through biological precipitation of minerals by a marine bivalve mollusk. While the specimen shown is a modern shell (Holocene), these are precursors to fossiliferous limestone. Found in shallow coastal estuarine environments with seagrass beds.
Uses & applications
Primary source of industrial lime when crushed; used in decorative arts, jewelry (mother-of-pearl), and as a calcium supplement in animal feed. Historically used as a food source and cultural symbol.
Geological facts
The scallop is the only bivalve that can swim by rapidly snapping its shells together to create jet propulsion. The ridges on the shell, called ribs, provide structural strength against predators and water pressure.
Field identification & locations
Identify by its fan shape, deep corrugated ribs (usually 17-22), and 'ears' (auricles) at the hinge. Commonly found on beaches along the Atlantic coast from Cape Cod to the Gulf of Mexico. Collectors look for unbroken valves with vibrant banding.
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