Banded iron formation was first discovered in northern Michigan in 1844, and mining of these deposits prompted the earliest studies of BIFs, such as those of Charles R. Van Hise and Charles Kenneth Leith. Iron mining operations on the Mesabi and Cuyuna Ranges evolved into enormous open pit mines, where steam shovels and other industrial machines could remove massive amounts of ore. Initially the mines exploited large beds of hematite and goethite weathered out of the banded iron formations, and some 2.5 billion tons of this "natural ore" had been extracted by 1980. By 1956 large-scale commercial production from the BIF itself began at the Peter Mitchell Mine near Babbitt, Minnesota. Production in Minnesota was 40 million tons of ore concentrate per year in 2016, which is about 75% of total U.S. production. Magnetite-rich banded iron formation, known locally as taconite, is ground to a powder, and the magnetite is separated with powerful magnets and pelletized for shipment and smelting.