sedimentary
Bivalve Shell Fragment (Biogenic Calcite/Aragonite)
Calcium carbonate (CaCO3, primarily aragonite/calcite)
AI-generated identification · may be incorrectHardness 3-3.5 on Mohs scale; dull to pearly luster; white to off-white with fine concentric growth lines; curved shell fragment morphology.
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Physical properties
Hardness 3-3.5 on Mohs scale; dull to pearly luster; white to off-white with fine concentric growth lines; curved shell fragment morphology.
Formation & geological history
Formed biologically through marine biomineralization by a bivalve mollusk, subsequently broken, tumbled, and smoothed by wave action in a coastal sedimentary environment.
Uses & applications
Source of sedimentary biogenic limestone, beach sand component, educational specimens, and shellcraft.
Geological facts
Thick shell fragments like this often originate from heavy-shelled surf clams (e.g., Spisula) eroded by high-energy coastal surf, illustrating how biological matter transforms into sedimentary rock components.
Field identification & locations
Identified by curved shell profile, concentric growth striations, and vigorous effervescence in dilute hydrochloric acid. Commonly found washed ashore on sandy ocean beaches.
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