Rock Identifier

fossil

Fossil Brachiopod or Mollusk Cast

Phylum Brachiopoda / Mollusca internal mold

AI-generated identification · may be incorrect

Hardness typically 3-5 on the Mohs scale depending on matrix (often calcite or quartz-replaced); reddish-brown to earthy tan color due to iron oxide staining; dull to earthy luster; irregular or bioclastic crystal structure.

Identified August 1, 2026More fossil →

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Physical properties

Hardness typically 3-5 on the Mohs scale depending on matrix (often calcite or quartz-replaced); reddish-brown to earthy tan color due to iron oxide staining; dull to earthy luster; irregular or bioclastic crystal structure.

Formation & geological history

Formed in ancient marine environments during the Paleozoic or Mesozoic eras, where shells were buried in sediment that later lithified into rock, leaving behind an internal mold or cast.

Uses & applications

Valuable for paleontological study, educational displays, and fossil collecting.

Geological facts

Fossil molds and casts provide crucial evidence of ancient marine biodiversity and help geologists date sedimentary strata relative to one another.

Field identification & locations

Look for distinct symmetrical shapes, beak structures, or impressions within sedimentary rock formations such as limestones or shales.

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Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

Likely fossil oyster shell (Fossilized bivalve shell; exact species cannot be identified from the image) — fossil

Likely fossil oyster shell

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

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

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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)

Rounded sedimentary pebble (Likely micritic limestone or calcareous sandstone) — sedimentary

Rounded sedimentary pebble

Likely micritic limestone or calcareous sandstone

Chert with Fossil Brachiopod (Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion) — sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion