Isle Royale greenstone, this state's official gem, is found on Isle Royale in Lake Superior
[DOC] [TLE] USGS Bulletin 1309 The geologic story of Isle Royale National Park [PAR] The bedrock sequence on Isle Royale consists of a thick pile of lava flows and .... 
in the United States east of the Rocky Mountains; at Isle Royale it is found only 
near ...