Copper

specimen number:
2013516

location:
Keweenaw Peninsula, Michigan, USA

description:
Bright lustrous well crystallized grouping of native copper with little attached matrix. Previously from the collection of Louis Lafayette. In great condition.

The Keweenaw Peninsula, stretching into Lake Superior from Upper Michigan, contains the largest known concentration of native copper on Earth. Geologically, this unique deposit is hosted within the Midcontinent Rift System, a billion-year-old tectonic feature where massive basaltic lava flows and interbedded conglomerates were deposited. During the Mesoproterozoic Era, hot, saline hydrothermal fluids migrated through these volcanic layers, leaching copper from the rocks and depositing it as pure metal within the gas bubbles of the basalt and the spaces between conglomerate pebbles. Historically, the region was first mined by indigenous peoples thousands of years ago, but the modern mining boom began in the 1840s following a report by Douglas Houghton. For over a century, the district was a global leader in copper production, fueling the American industrial revolution and the electrification of the country until the last major mines closed in the late 1960s.

For mineral collectors, the Keweenaw is the ultimate locality for native copper specimens, prized for their diverse and aesthetic forms. The copper occurs in several distinct habits, including sharp spinel-law twin crystals, dendritic "feather" shapes, and massive "float" copper transported by glaciers. These specimens are often found in association with a variety of secondary minerals such as bright green epidote, white to pinkish calcite, and rare "halfbreed" specimens where native copper and native silver are physically joined in a single piece. The "amygdaloid" lodes are particularly famous for producing small, lustrous crystals within the cavities of the volcanic rock, while the conglomerate lodes often yielded massive, heavy sheets of metal. Today, while industrial mining has ceased, the Keweenaw remains a pilgrimage site for mineral enthusiasts, with its historic mine dumps and museum collections preserving the legacy of the "Copper Country" as one of the most significant mineralogical regions in the world.

Questions about this specimen?
Send an email or call us: 314-341-1811.