Copper

specimen number:
1791318

location:
Keweenaw Peninsula, Michigan, USA

description:
Well crystallized native copper, the largest measuring to 0.5 cm in size, on matrix. In great condition. Minor calcite is present.

Copper mining in the Keweenaw Peninsula of Michigan has a rich history spanning from pre-Columbian native copper extraction by indigenous peoples to a massive industrial boom that began in the mid-19th century, particularly following the Douglas Houghton geological report of 1841 and the subsequent mining rush of 1843. Geologically, the region is defined by the Keweenawan Rift System, a vast series of mid-Proterozoic basaltic lava flows and interbedded sedimentary conglomerate layers where native copper precipitated from hydrothermal fluids into open cavities, amygdules, and fracture zones. Mineralogically, the district is globally renowned for its massive, pure native copper masses alongside associated minerals such as crystallized native silver, datolite nodules, epidote, prehnite, and various zeolites, establishing it as one of the world's most unique and productive copper provinces before most major operations wound down by the late 20th century.

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