fossil

Fossilized crinoid stem segment

Crinoidea fossil, commonly columnal ossicle of Paleozoic crinoid

AI-generated identification · may be incorrect

Cream-white crystalline calcite with a radiating, star-like central pattern and darker weathered exterior; Mohs hardness about 3, vitreous to dull luster, rhombohedral calcite cleavage, and specific gravity near 2.7. The specimen appears tumbled or naturally rounded.

Identified September 8, 2026More fossil →

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Physical properties

Formation & geological history

Crinoid skeletal plates were originally high-magnesium calcite and accumulated in shallow marine carbonate sediments, commonly during the Mississippian–Pennsylvanian (about 359–299 million years ago); later lithification and recrystallization preserved the segment.

Uses & applications

Primarily a teaching, collecting, and decorative specimen; polished crinoid fossils are used in jewelry and cabochons, but it has little industrial value.

Geological facts

The star-shaped lumen is characteristic of many crinoid columnals and reflects the animal’s stalk anatomy, not a crystal growth pattern. Crinoids are echinoderms related to modern sea lilies and feather stars.

Field identification & locations

Identify by the circular segmented form, radial symmetry, and calcite reaction to dilute hydrochloric acid; common in Paleozoic limestones of the Midwestern and central United States, especially Indiana, Iowa, Missouri, and Kansas.