The 17-ton native copper slab exhibited in the Copper Pavilion was discovered in 1991 and recovered in 2001 from the bottomlands near the shore of Lake Superior. It holds a Guinness World Record. It is slab shape because it was once part of a vein or a fracture in the bedrock that filled with minerals as a result of precipitation from hot waters. The large slab was not transported by the glacier and is not “float” copper. It is on permanent loan from the State of Michigan, Department of Natural Resources. The smaller 550-pound smoothed mass of native copper also on exhibit was found nearby.
Read more about the discovery and geology of the Copper Slab.
“Float” copper is glacially transported and during this transport the irregular mass of native copper is physically sculpted by interaction with rocks also being carried in the glacial ice. The malleable native copper tends to be shaped into smooth blob-like masses. Regular rocks become rounded into boulders by physical contact with one another.
Read more about Float Copper Geology.
While the large slab of native copper on exhibit in the Copper Pavilion is impressive, single masses of native copper weighing up to 400 tons were found in the mines.