Copper

specimen number:
8911098

location:
Cliff Mine, Keweenaw Co., Michigan, USA

description:
A choice loose example of what is known as a copper skull. These usually do not form such good small examples. In great condition. The specimen comes with previous labels from the collection of Martin Zinn and the Alton collection.

The Cliff Mine, located in Keweenaw County, Michigan, sits along the native copper deposits of the Precambrian Keweenaw Rift, where ancient lava flows and sedimentary layers trapped pure metallic copper in fissures and vein networks. Opened commercially in 1845, it became the first financially successful native copper mine in North America, proving that the region could produce massive native metal rather than standard sulfur-bearing ores, and generating substantial dividends for its investors until major operations ceased in the late 1800s. Among the most remarkable mineral specimens recovered from the site and surrounding native copper deposits are native copper "skulls" or copper shells. These unusual formations are hollow, rounded shells of native copper that formed when molten lava or copper-rich fluids flowed around organic matter or existing rocks, or when copper precipitated directly as a crust over rounded basalt, cobbles, or altered pebble inclusions within conglomerate layers. Over time, the softer inner stone or material weathered away or dissolved, leaving behind a hollow, dome-shaped metallic shell that resembles a skull. Today, specimens from the Cliff Mine dumps are prized historical artifacts, and these native copper skulls remain exceptionally rare examples of the unique geological processes that occurred in the Lake Superior region.

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