Calcite with Quartz

specimen number:
2062177

location:
Isle Royale Mine, Houghton Co., Michigan, USA

description:
Colorless gemmy and lustrous scalenohedral crystals of calcite to 2.5 cm in size in an open pocket lined with crystallized quartz. The quartz is an orange red in color due to the presence of iron oxide. In great condition. Collected in August, 1998.

The Isle Royale Mine, located south of Houghton in the Keweenaw Peninsula of Michigan, was one of the most prominent operations in the Lake Superior copper district. Geologically, the mine exploited the Isle Royale Lode, a mineralized amygdaloid bed within the Portage Lake Volcanics characterized by native copper filling the gas vesicles of ancient basaltic lava flows. Unlike the conglomerate mines to the north, this deposit relied on the occurrence of copper within the epidote-rich and chloritic altered basalt, often producing magnificent specimens of crystallized native copper and silver. Historically, the Isle Royale Mining Company was organized in 1852, with the mine operating through several periods of restructuring and consolidation, most notably under the control of the Calumet and Hecla Mining Company in the early 20th century. The mine saw its most productive years between 1899 and 1937, eventually closing in 1948 after a century of contributing to the industrial growth of the Copper Country. Today, the site is recognized for its extensive waste rock piles which remain a favorite for mineral collectors and as a significant part of the Keweenaw National Historical Park landscape.

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