sedimentary

Fossiliferous limestone (probable crinoidal limestone)

Calcite-rich carbonate rock; chiefly CaCO₃, with fossil crinoid fragments

AI-generated identification · may be incorrect

Gray-brown, coarse to fine crystalline texture with visible circular/columnar fossil fragments; calcite has Mohs hardness 3, vitreous to dull luster, rhombohedral cleavage, and specific gravity about 2.7. Effervesces strongly with dilute hydrochloric acid or vinegar if the surface is fresh.

Identified September 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from accumulated marine skeletal debris, commonly during Paleozoic seas (roughly 541–252 million years ago), then compacted and cemented. Exact age cannot be determined from the photograph alone.

Uses & applications

Used as crushed aggregate, cement and lime feedstock, building stone, and educational/collecting material; attractive polished pieces may be decorative but are generally not jewelry-grade.

Geological facts

The round patterned inclusions likely represent crinoid columnals, often called “stone lilies.” Weathering can make fossil fragments stand out in relief against the carbonate matrix.

Field identification & locations

Look for repeated disk- or star-shaped fossil sections and test for acid reaction; a hand lens can distinguish crinoids from shell fragments. Common in Paleozoic marine limestone deposits worldwide, especially the Midwestern United States and parts of Europe.