Rock Identifier
Fossilized bivalve or brachiopod shell (Indeterminate calcitic shell fossil; likely Bivalvia or Brachiopoda) — fossil
fossil

Fossilized bivalve or brachiopod shell

Indeterminate calcitic shell fossil; likely Bivalvia or Brachiopoda

AI-generated identification · may be incorrect

Pale gray-white, strongly ribbed, rounded shell fragment with dull to slightly pearly luster; composed mainly of calcite (CaCO₃), Mohs hardness about 3, with possible cleavage inherited from calcite. The regular growth ribs and shell symmetry are characteristic of a marine fossil.

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Physical properties

Pale gray-white, strongly ribbed, rounded shell fragment with dull to slightly pearly luster; composed mainly of calcite (CaCO₃), Mohs hardness about 3, with possible cleavage inherited from calcite. The regular growth ribs and shell symmetry are characteristic of a marine fossil.

Formation & geological history

Formed by a marine mollusk or brachiopod, then buried and mineralized through replacement or infilling by calcite-rich sediment. Exact geological age cannot be determined from the image, but such specimens range from Paleozoic to Cenozoic strata.

Uses & applications

Used primarily for education, fossil collecting, and display; not generally suitable for jewelry or construction. Value is mainly aesthetic, taxonomic, and provenance-dependent.

Geological facts

The visible concentric ridges are growth lines, recording successive shell expansion. Brachiopods often have bilateral shell asymmetry, whereas bivalves typically show more obvious hinge-related shape differences.

Field identification & locations

Common in marine limestone and shale worldwide; identify by shell symmetry, hinge form, rib pattern, and reaction to dilute hydrochloric acid, which effervesces on calcite. The image is insufficient for confident genus-level identification.

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