One of 83 counties in Michigan, United States. County seat: Eagle River. Situated on the Keweenaw Peninsula on Michigan's Upper Peninsula, it also includes Isle Royale in Lake Superior, which was a separate county during the 19th century.

(geology) The younger division of the Proterozoic eon as represented by rocks in the Great Lakes region of the United States

(mineralogy) A copper ore and discredited mineral species composed of arsenic, copper, nickel, and cobalt.