Sedimentary

Crinoidal Limestone

Bioclastic Limestone

Hardness 3 (Mohs scale), typically gray to black matrix with white to light gray fossil inclusions. Luster is dull to slightly shiny when polished.

Identified June 17, 2026More sedimentary →

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Physical properties

Hardness 3 (Mohs scale), typically gray to black matrix with white to light gray fossil inclusions. Luster is dull to slightly shiny when polished.

Formation & geological history

Formed in marine environments from the accumulation of calcium carbonate and fossilized remains of crinoids (sea lilies) and other marine organisms, often dating back to the Paleozoic era (e.g., Mississippian or Pennsylvanian periods).

Uses & applications

Used in construction, as ornamental stone, and shaped into jewelry, focal beads, or tumbled stones for collectors.

Geological facts

Crinoids are marine animals related to starfish and sea urchins. Their stem segments, often referred to as 'Indian beads', are common fossils found in these limestones.

Field identification & locations

Easily identifiable by the distinct circular or columnar fossil fragments (crinoid stems) embedded in the limestone matrix. Often found in areas that were once shallow ancient seas, such as the Midwestern United States.