Copper

specimen number:
2062110

location:
Keweeenaw Peninsula, Michigan, USA

description:
A branching crystallized grouping of native copper crystals, some of these extremely large and measuring to 3.0 cm in size. Very little attached matrix, this is in terrific condition.

Mining in the Keweenaw Peninsula of Michigan has a long and significant history centered on native copper deposits formed within ancient volcanic rocks of the Midcontinent Rift. These deposits occur primarily in amygdaloidal basalt flows and conglomerate beds, where native copper was deposited by hydrothermal processes and later concentrated in fractures and cavities. Mining began in the 1840s and rapidly expanded as rich deposits were discovered, leading to the development of major mines such as the Quincy, Calumet and Hecla, and Cliff. Both fissure veins and stratiform deposits were worked through extensive underground operations, with some shafts reaching great depths. The region became one of the leading copper producing areas in the United States during the 19th and early 20th centuries. Mining declined in the early to mid 20th century as ore grades decreased and competition increased, but the Keweenaw Peninsula remains historically important and is well known for its distinctive native copper specimens.

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