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Earth Treasures: Petoskey Stone

By Chisom Ibemere

Petoskey stone is composed of fossilized coral that is found specifically in Michigan, USA. It is known as both a rock and a fossil which is mostly pebble shaped. It’s name is gotten from the city of Petoskey, where it was first discovered.

The stone was formed during the Devonian period, around 350 million years ago, when Michigan was covered by a warm, shallow sea.

Petoskey stone is often polished and used as a decorative stone in jewelry, artwork, and ornamental objects. They are used in souvenir items, such as keychains, magnets, and pendants.

Petoskey stone is a type of fossilized coral, specifically a colony coral known as Hexagonaria percarinata. It is composed primarily of calcite, a form of calcium carbonate.

It is characterized by its honeycomb-like pattern of hexagonal shapes, which are the fossilized remains of coral polyps. The stone is usually light gray or white, but it can also exhibit other colors due to impurities or mineral inclusions.

It has a hardness of around 4 on the Mohs scale, and is often porous and can absorb oils or liquids if not properly sealed or treated. It is highly valued for its unique pattern of hexagonal coral fossilization.

The value of Petoskey stone is primarily sentimental and aesthetic. Its iconic appearance and association with Michigan make it highly valued among residents and visitors as a piece of natural history and a symbol of the state.


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