Rock Identifier
Fossiliferous Limestone (Gastropod / Crinoid Fossil Rock) (Biogenic Sedimentary Rock (CaCO3)) — fossil
fossil

Fossiliferous Limestone (Gastropod / Crinoid Fossil Rock)

Biogenic Sedimentary Rock (CaCO3)

Hardness: 3-4 on Mohs scale. Color: Reddish-brown, tan, and cream matrix with lighter fossil inclusions. Luster: Dull to vitreous when wet/polished. Structure: Fine-grained matrix packed with calcified marine fossils (gastropods, crinoid fragments, or shells).

Hardness
3-4 on Mohs scale
Luster
Dull to vitreous when wet/polished
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Physical properties

Hardness: 3-4 on Mohs scale. Color: Reddish-brown, tan, and cream matrix with lighter fossil inclusions. Luster: Dull to vitreous when wet/polished. Structure: Fine-grained matrix packed with calcified marine fossils (gastropods, crinoid fragments, or shells).

Formation & geological history

Formed during the Paleozoic or Mesozoic era in shallow, warm marine environments where ancient marine organisms accumulated on the seafloor and were compacted and cemented into limestone over millions of years. Iron oxide staining gives the matrix its reddish-brown hue.

Uses & applications

Popular as decorative river rocks, landscape stones, educational display specimens, polished gemstones, and lapidary art.

Geological facts

This specimen displays abundant fossil cross-sections, particularly coiled gastropod shells and rounded crinoid stem fragments, preserved within an iron-rich limestone or cherty matrix.

Field identification & locations

Identified by the distinct circular, spiral, and crescent-shaped white-to-tan fossil cross-sections embedded within a darker reddish matrix. Commonly found along riverbeds, lake shores (such as the Great Lakes region), and ancient sea beds.

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