05/30/2026
Isle Royale Greenstone is Michigan's official state gem and one of the most distinctive and most geologically significant minerals found anywhere in the Great Lakes region, a form of chlorastrolite found almost exclusively on Isle Royale and the Keweenaw Peninsula in concentrations that exist nowhere else on Earth in comparable quality or abundance. The stone produces a turtleback pattern of radiating green and gray crystals that gives it an appearance unlike any other gem in North America, a mosaic of interlocking mineral growth that formed over a billion years ago in the volcanic basalt flows that created the Lake Superior basin.
The green color and the distinctive pattern come from the specific mineral composition and the conditions under which the stone formed, ancient lava flows cooling slowly enough to allow the chlorastrolite crystals to develop their characteristic radiating structure. Superior's waves then did the work of tumbling and smoothing the stones over thousands of years and depositing them on the shores of Isle Royale where collectors have been finding them since the 19th century.
Greenstone collecting on Isle Royale requires a permit and carries strict size limitations because the resource is finite and the National Park Service takes its protection seriously. The best specimens are small, dense, and brilliantly patterned, and finding a quality greenstone on the island's rocky shores produces the specific satisfaction of discovering something genuinely rare in the place it has always belonged. Michigan named it the state gem in 1972 and the designation fits perfectly. Isle Royale Greenstone is beautiful, ancient, specific to Michigan, and found almost nowhere else. That is exactly what a state gem should be.
