sedimentary
Fossilized Coral (Petoskey Stone or similar Hexagonaria variant)
Hexagonaria percarinata (Fossilized Coral)
Hardness 3 (calcite) to 7 (if silicified), distinctive hexagonal/circular coral polyp patterns with radiating lines, reddish/brownish color varying with mineral impurities, typically dull to vitreous luster when polished.
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Physical properties
Hardness 3 (calcite) to 7 (if silicified), distinctive hexagonal/circular coral polyp patterns with radiating lines, reddish/brownish color varying with mineral impurities, typically dull to vitreous luster when polished.
Formation & geological history
Formed in warm shallow seas during the Devonian Period (approx. 350-400 million years ago) from the fossilization of rugose coral.
Uses & applications
Commonly used in lapidary, cut into cabochons for jewelry (as seen here with the drilled hole), and collected as a fossil specimen.
Geological facts
Petoskey stones are the state stone of Michigan. The distinct pattern is the fossilized exoskeleton of individual coral polyps.
Field identification & locations
Identify by the characteristic hexagon or circle-like patterns containing radiating lines (corallites). Found in limestone deposits, notably around the Great Lakes region (Michigan) or Indonesia depending on the specific type.
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