Petoskey stone

A Petoskey Stone is a particular type of calcite stone, usually found in the northern part of Michigan's lower peninsula. It is the fossilization of the coral Hexagonaria percarinata. It only occurs in the Gravel Point Formation of the Traverse Group of the Devonian Age stone. The stone looks normal when dry; but when wet, a distinctive mottled pattern of the fossil emerges. It is named after Petoskey, Michigan where it is often found. It is the official state stone of Michigan.

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