Petoskey stone

Locations: Stones can be found on various beaches in Northern Michigan with many of the most popular being those surrounding Petoskey and Charlevoix. Similar fossil corals occur in a variety of locations, however the name Petoskey stone should only be applied to those from Northern Michigan.

Hardness: 3

Petoskey stone is a rock and a fossil, often pebble-shaped, that is composed of a fossilized coral, Hexagonaria percarinata. The stones were formed as a result of glaciation, in which sheets of ice plucked stones from the bedrock, grinding off their rough edges and depositing them in the northwestern portion of Michigan's lower peninsula.