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May-June 2013

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Pink Petoskey Stones from Northern Michigan

Petoskey stones have been collected in northern Michigan for more than a century and are familiar to many collectors. Composed of calcite, the Petoskey stone is actually a Devonian-age fossil coral with a distinctive hexagonal pattern consisting of small six-sided chambers in which corals once lived approximately 350 million years ago when the Michigan Basin was under a sea. Petoskey stones comprise several species of the genus Hexagonaria; although they occur in slightly different sizes and shapes, all show hexagonal patterns. Of these, Hexagonaria percarinata is perhaps the most common. In 1965 the Petoskey stone was declared the official state stone of Michigan by the passage of Michigan State Legislature House Bill 2297. Petoskey stones have been collected along the eastern shoreline of Lake Michigan for years, particularly in the Petoskey-Charlevoix area, where they once occurred in abundance. Although small stones may still be found on the beaches, larger and better specimens are more easily obtained today from gravel pits and cut-banks along the county highways farther inland. For more information on collecting Petoskey stones and how to polish them, see Mueller and Wilde (2004).

Dr. George W. Robinson is the curator of the A. E. Seaman Mineral Museum and a professor of mineralogy in the Department of Geological and Mining Engineering and Sciences at Michigan Technological University.

Donald Reed is an avid collector, lapidary, and wire jewelry artist residing in northwestern Lower Michigan.

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