sedimentary

Fossiliferous Limestone (Crinoid stem)

CaCO3 (Calcium Carbonate) with Fossil Inclusions

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale), Color: light grey to cream, Luster: dull to earthy, Crystal structure: rhombohedral (microcrystalline calcite), Cleavage: perfect rhombohedral in calcite matrix, Specific gravity: 2.71

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments from the accumulation of organic debris such as shell, coral, algal, and fecal debris. These fossils often date from the Paleozoic era (approx. 250-500 million years ago).

Uses & applications

Used in the production of cement, as a building stone (dimension stone), in road construction, and the fossil specimens are popular for educational purposes and amateur collectors.

Geological facts

Crinoids are also known as 'sea lilies' and are related to starfish and sea urchins. The small cylindrical segments in the rock are parts of the stem that once anchored the animal to the sea floor.

Field identification & locations

Identify by a grey, fine-grained matrix that fizzes when exposed to warm diluted acid (HCl). Look for circular or disc-shaped impressions (crinoid columnals). Often found in limestone outcrops, quarries, and riverbeds across the Midwestern USA.