Rock Identifier
Fossiliferous pebble, possibly a crinoid or shell fragment (Indeterminate bioclast in a dark sedimentary matrix; likely carbonate fossil material (calcite, CaCO₃)) — fossil
fossil

Fossiliferous pebble, possibly a crinoid or shell fragment

Indeterminate bioclast in a dark sedimentary matrix; likely carbonate fossil material (calcite, CaCO₃)

AI-generated identification · may be incorrect

Small rounded dark-gray pebble with a contrasting cream, porous fossil-like inclusion. The matrix may be fine-grained limestone or chert; calcitic fossil material is Mohs 3 and commonly dull to slightly waxy, but hardness and acid reaction are unverified.

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Physical properties

Small rounded dark-gray pebble with a contrasting cream, porous fossil-like inclusion. The matrix may be fine-grained limestone or chert; calcitic fossil material is Mohs 3 and commonly dull to slightly waxy, but hardness and acid reaction are unverified.

Formation & geological history

Likely formed when marine skeletal debris was buried, mineralized, and cemented in carbonate sediment, then rounded by erosion. Exact geological age cannot be determined from the photograph; marine Paleozoic–Mesozoic rocks are common possibilities.

Uses & applications

Primarily a teaching or collecting specimen; not suitable for construction or jewelry except as a polished curiosity. Typical value is modest.

Geological facts

The pale structure could be a crinoid segment, shell fragment, or weathered coral, but the image is insufficient for confident identification.

Field identification & locations

Look for repeated chambers, radial symmetry, or shell growth lines; a dilute hydrochloric-acid test may fizz on calcite. Common sources include marine limestone gravels and fossil-bearing coastal or river deposits.

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Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

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Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

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Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

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