fossil

Fossil coral pebble

Fossilized colonial coral, commonly Favosites or Hexagonaria

AI-generated identification · may be incorrect

Gray, rounded, fine honeycomb-like corallite pattern; typically calcite replacing original aragonite. Mohs hardness about 3–4, dull to waxy luster, no obvious cleavage, and specific gravity around 2.6–2.8.

Identified September 12, 2026More fossil →

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Physical properties

Formation & geological history

A Paleozoic colonial coral fossil preserved by burial and mineral replacement, then naturally rounded by erosion or water transport. Exact age and genus require a clearer view of the coral structure and locality.

Uses & applications

Primarily a collector specimen, educational material, or polished ornamental stone; not generally used structurally. Some varieties are sold as fossil coral jewelry and cabochons.

Geological facts

The repeated polygonal or tubular pattern represents individual coral corallites, not crystal grains. Hexagonaria fossils are famously associated with Michigan’s state stone, Petoskey stone.

Field identification & locations

Identify by the consistent cellular pattern across the surface and its gray limestone-like appearance; vinegar may weakly fizz if calcitic. Common in Paleozoic limestone deposits and glacial gravels of the Great Lakes region.