This event is in the "Everyone" group. Petoskey Stone Polishing Kit All Day Everyone All Branches Virtual Event This event is in the "Everyone" group. Jul 16 2024 Tue Petoskey Stone Polishing Kit All Day All Branches Please note you are looking at an event that has already happened. Library Branch: All Branches Age Group: Everyone Program Type: Arts & Crafts Program Description: Michigan designated the Petoskey stone as the official state stone in 1965. The Petoskey stone (Hexagonaria pericarinata) is not a stone but a fossilized coral.