Calcite with Copper

specimen number:
2013513

location:
Quincy Mine, Houghton Co., Michigan, USA

description:
Classic specimen from Michigan consisting of a scalenohedral semi lustrous mostly gemmy calcite crystal, this with inclusions of native copper throughout. In good condition with very minimal cleaving present. The condition on this is much better than on most.

The Quincy Mine, located on the Keweenaw Peninsula in Houghton County, Michigan, is a legendary copper deposit situated within the Portage Lake Volcanics. Geologically, it occupies a series of Neoproterozoic basaltic lava flows where native copper was deposited within the amygdaloidal flow tops and interbedded conglomerates. This mineralization occurred approximately 1.1 billion years ago as hot, metal-bearing fluids migrated through the volcanic stack during the Midcontinent Rift. Historically, the Quincy Mining Company was incorporated in 1848 and earned the nickname "Old Reliable" for its consistent production and dividend payments over nearly a century. The mine was a marvel of 19th-century engineering, eventually reaching depths of over 9000 feet along the dip of the Pewabic Lode before primary operations ceased in 1945.

For mineral collectors, the Quincy Mine is world-famous for its exceptional "copper-in-calcite" specimens. These unique pieces feature sharp, transparent to milky white calcite crystals that contain delicate inclusions of bright, native copper, often forming dendritic or leafy shapes frozen within the crystal lattice. The calcite typically occurs in scalenohedral or rhombohedral habits and was deposited by late-stage hydrothermal fluids in the open vugs of the basalt. These specimens are highly prized for the dramatic visual contrast between the metallic red of the copper and the vitreous luster of the host calcite. Today, the Quincy Mine is a National Historic Landmark, and while the deep underground workings are flooded, the historic specimens preserved in museums remain the definitive standard for this rare and beautiful mineral association.

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