Calcite with Copper

Unknown Owner

A classic scalenohedral calcite crystal 4.3 cm in height coming off matrix with crystallized native copper. The calcite crystal has inclusions of native copper throughout. This one is in good condition with just very slight micro-cleaving present.The Mass Mine, located in Ontonagon County near the town of Mass City, Michigan, was a significant producer of native copper in the Adventure district of the Keweenaw Peninsula. Geologically, the mine was unique for exploiting several parallel mineralized horizons simultaneously, including the Knowlton, Evergreen, South Evergreen, and Ogima amygdaloid lodes within the Portage Lake Volcanics. These basaltic flows contained copper as both fine grains within amygdules and as massive "mass copper" boulders weighing several tons, often associated with minerals like datolite and epidote. Historically, the Mass Consolidated Mining Company was formed in 1899 through the merger of several smaller, mid-19th century ventures, including the original Mass, Ridge, and Ogima mines. The consolidated operation saw its peak production during the early 20th century, particularly between 1902 and 1919, before high costs and declining ore grades led to its closure in 1928. Today, the mine is celebrated as a classic Michigan locality, and its extensive waste piles remain a popular site for collectors seeking native copper and the colorful datolite nodules for which the district is famous.