Petoskey Stones are masses of fossil colony coral, Hexagonaria percarinata. They occur abundantly in Devonian reef limestones of the Traverse Group in the northern part of the Southern Peninsula. The Devonian Period was about 350 million years ago. Coral groups weathered out of the limestone were widely scattered by Pleistocene glacial action. They are readily found on beaches and in gravel deposits as pebbles and cobbles rounded by erosion. Petoskey is the English adaptation of either "Be-dos-e-gay" or "Petosegay," an Ottawa Indian word and variant meaning "sun rays of the dawn."

For more Information about the State stone please see Petoskey Stone 4 page handout (590 KB).

Michigan's State Gem - Chlorastrolite

Chlorastrolite, also commonly called Isle Royal greenstone, is a variety of the mineral pumpellyite. It is found chiefly as bean-sized, rounded beach pebbles. Chlorastrolite is an opaque, usually bluish-green stone with a finely radiating or star-like pattern of slender crystals. It displays a unique mottling of dark green "eyes" ringed with pale green which results in a "turtle back" pattern.

For more Information about the State Gem please see  Greenstone (30 KB).