Petoskey stone

Uncommon card · No. 164670

A Petoskey stone ( pə-TOSS-kee) is a collectible rock composed of the fossilized rugose coral, Hexagonaria percarinata. It is usually found pebble-shaped; such stones were formed as a result of glaciation, in which sheets of ice plucked the fossilized corals from the bedrock, ground off their rough edges and deposited them in the northwestern (and some in the northeastern) portion of Michigan's lower peninsula. In those same areas of Michigan, complete fossilized coral colony heads can be found in the source rocks for the Petoskey stones. 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, approximately 350 million years ago. When dry, the stone resembles ordinary limestone but when wet or polished using lapidary techniques, it reveals the distinctive mottled pattern of the six-sided coral fossils. It is sometimes made into decorative objects, or even used as a gemstone...

Read on Wikipedia · Image David J. Fred (Dfred), CC BY 3.0