fossil

Fossil Brachiopod or Mollusk Cast

Phylum Brachiopoda / Mollusca internal mold

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

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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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

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