fossil

Tumbled fossiliferous limestone

Crinoidal limestone, chiefly calcite (CaCO₃), with fossil echinoderm fragments

AI-generated identification · may be incorrect

Typically Mohs hardness 3, opaque, gray to cream with dark branching or segmented fossil patterns, and a dull to waxy polish. Calcite has trigonal crystal structure and perfect rhombohedral cleavage, though individual grains are usually microscopic.

Identified August 22, 2026More fossil →

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Physical properties

Formation & geological history

Formed when marine skeletal debris, especially crinoid ossicles, accumulated and lithified on Paleozoic shallow-marine seafloors, commonly during the Ordovician–Mississippian periods (about 485–323 million years ago).

Uses & applications

Used as a decorative tumbled stone, teaching specimen, and occasionally as ornamental or building limestone; it is not generally used as a gemstone.

Geological facts

The branching marks are commonly cross-sections of crinoid stems, often called “star stone” when five-part segments are visible. Dilute hydrochloric acid or vinegar produces effervescence from calcite.

Field identification & locations

Identify it by abundant fossil fragments, moderate softness, and acid reaction; common sources include Indiana and other Paleozoic limestone regions of North America, plus parts of Europe. The image could also represent a fossil-rich polished limestone rather than a single fossil.