sedimentary

Tumbled fossiliferous limestone

Bioclastic limestone, likely crinoidal or shell-rich limestone (calcite, CaCO₃)

AI-generated identification · may be incorrect

Gray, fine-grained carbonate matrix with elongated tan fossil fragments and a polished luster; calcite has Mohs hardness 3, rhombohedral cleavage, and specific gravity about 2.7. Effervesces with dilute hydrochloric acid or strong vinegar, especially on a freshly scratched surface.

Identified September 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when marine skeletal debris accumulated, was compacted, and cemented on an ancient seafloor, commonly during the Paleozoic Era (about 541–252 million years ago). Later tumbling and polishing produced the smooth shape.

Uses & applications

Used as a decorative stone, cabochon, paperweight, and educational fossil specimen; limestone is also important in cement, aggregate, and construction.

Geological facts

The elongated inclusions may be crinoid stem segments or fossil shell fragments, but exact identification requires close examination or microscopy.

Field identification & locations

Look for visible fossil fragments, gray carbonate matrix, relatively low hardness, and acid reaction; common sources include Midwestern and European Paleozoic limestone deposits. Avoid prolonged acids, which etch the polish.