Outdoors: Petoskey stones

Jul 8, 2020

Visual artists always have been aware of geometric shapes. 

The Great Masters were all about geometry. 

Pablo Picasso captured  his world in shapes.  M. C. Escher combined shapes with his tessellating designs, and architect Buckminster Fuller demonstrated that tessellating triangles form a hexagon, which is a shape with great structural strength.

This structural strength is demonstrated by  a coral fossil we call a Petoskey stone. 

Petoskey stones are fragments of a reef made up of colonies of corals dating back some 350 million years to a time when Michigan was covered by shallow tropical seas.

The scientific name is Hexagonaria because each individual coral polyp secreted a six-sided skeleton made of calcium carbonate, which it shared with the six adjacent polyps in the colony.

The soft-bodied coral animals , which were probably quite colorful, were not preserved. As seas came and went during geologic history, the  hexagon-shaped skeletons were buried in sediment. Durable minerals replaced the calcium carbonate, resulting in grey fossils.

During the Ice Ages, some of the bedrock was scraped up by glaciers. Now, the Lower Peninsula of Michigan is covered with glacial debris, with Petoskey stones and other fossils  scattered randomly.

You may read that the Petoskey stone is found only along the Lake Michigan Shoreline near Traverse Bay.

But we know differently.

Traveling home in the suitcases of Interlochen campers, these hexagon-shaped fossils have been spread throughout the world!