Fossilized Coral (Petoskey Stone or similar)

Physical Properties

Hardness: 3-4 (Mohs scale), Color: Cream, beige, or white when unpolished, Luster: Dull to earthy (waxy if polished), Structure: Visible radial septa and hexagonal or honeycomb-like patterns.

Formation & Geological History

Formed from the fossilized remains of ancient colonial corals from the Devonian period (approx. 350-400 million years ago) in shallow marine environments.

Uses & Applications

Commonly used for lapidary work, jewelry, home decor, and educational geological collections.

Geological Facts

The state stone of Michigan is the Petoskey stone, which is this specific type of fossilized rugose coral. These corals were once part of a reef in a warm, shallow sea covering North America.

Field Identification & Locations

Look for the distinctive 'sunburst' or honeycomb pattern on the surface. These are frequently found along shorelines of the Great Lakes, especially when the stone is wet.

Identified on: 4/19/2026

Mode: Standard