petoskey stones on the beach2, photo by jimevans_2000.

In the summertime in northwest Michigan, almost any Lake Michigan beach will have a person or two slowly walking or wading their way along the beach, gathering Petoskey stones in a bucket.

While I don’t begrudge anyone the extra money from harvesting them or the simple pleasure of finding, I do get a little peeved that there are times when I can’t find one to show a visitor or child who has never seen one. In honor of that, I am hereby creating Throw in Petoskey Stone Day, wherein participants head to a likely beach, look for Petoskey stones and then throw them way out in the water so that folks in the months or years to come can find them. It takes place every year on the third Saturday of July – tomorrow this year and Saturday, July 17 2010 if you’re the planning ahead sort.

Wikipedia’s Petoskey stone entry says:

A Petoskey stone is a rock and a fossil, often pebble-shaped, that is composed of a fossilized coral, Hexagonaria percarinata. The stones were formed as a result of glaciation, in which sheets of ice plucked stones from the bedrock, grinding off their rough edges and depositing them in the northwestern portion of Michigan’s lower peninsula.

Petoskey stones are found in the Gravel Point Formation of the Traverse Group. They are fragments of a coral reef that was originally deposited during the Devonian period, about 350 million years ago. When dry the stone resembles ordinary limestone but when wet or polished using lapidary techniques, the distinctive mottled pattern of the fossil emerges. It is sometimes made into decorative objects. Other forms of fossilized coral are also found in the same location.

In 1965, it was named the state stone of Michigan.

You can learn more about the name of the Petoskey stone from Rose Petoskey.

Jim found these on the Lake Michigan shore near Watervale (an amazing resort). Be sure to check this photo out bigger.