Polished Petoskey Stone Value Guide

The Polished Petoskey Stone is a 350-million-year-old fossilized colonial coral known as Hexagonaria percarinata, unique to the shores of Lake Michigan. Designated as Michigan's state stone in 1965, these specimens are highly collectible for their intricate hexagonal patterns that emerge vividly once the calcite-rich surface is rounded and polished.

What affects the value of Polished Petoskey Stone?

• Clarity and definition of the hexagonal coral structure across the entire surface.
• The quality of the hand or machine polish, ensuring no deep scratches or dull spots remain.
• Overall size and weight of the palm stone, with larger, well-preserved specimens commanding higher prices.
• The contrast between the fossilized cells and the surrounding matrix, which enhances visual appeal.

How to Identify Polished Petoskey Stone?

• Look for the distinct 'six-sided' or hexagonal cell pattern characteristic of colonial coral.
• Verify the presence of a dark 'eye' or center within each individual cell of the fossil.
• Check for a smooth, glass-like finish that reveals the pattern, as unpolished stones appear like ordinary gray limestone.
• Confirm the material is calcite-based, which is typical for authentic Devonian period fossils from the Great Lakes region.

History of Polished Petoskey Stone

Petoskey stones are fragments of a coral reef that was deposited during the Devonian period, approximately 350 million years ago. These fossils are unique to the shores of the Great Lakes, specifically Lake Michigan. They were designated as the state stone of Michigan in 1965.