Petoskey Stone Cabochon Value Guide

This polished circular cabochon is a 350-million-year-old relic of the Devonian Period, formed from fossilized rugose coral colonies. As Michigan's official state stone, these specimens are highly collectible for their distinct hexagonal patterns and deep connection to the ancient warm seas of the United States.

What affects the value of Petoskey Stone Cabochon?

• Clarity and definition of the hexagonal coral patterns across the surface.
• Quality of the polish and absence of surface pits or natural fractures.
• Size and symmetry of the circular cabochon cut.
• Contrast between the fossilized coral structures and the surrounding matrix.

How to Identify Petoskey Stone Cabochon?

• Look for the distinct six-sided 'honeycomb' or hexagonal pattern characteristic of Hexagonaria percarinata.
• Verify the presence of a dark 'eye' or center within each individual coral cell when polished.
• Check for a smooth, glass-like finish that reveals the intricate calcite structure of the fossil.
• Ensure the stone reacts to a dilute acid test, as authentic Petoskey stones are composed of calcite.

History of Petoskey Stone Cabochon

These unique stones are fossilized colonies of Hexagonaria percarinata, a type of rugose coral that lived in the warm Michigan seas during the Devonian period, roughly 350 million years ago. Named after Chief Pet-O-Sega, they became the state stone of Michigan in 1965.