At least 200 have been found, and extracted out of deep rock at the Wonderstone Silver Mine in South Africa, averaging 1-4 inches in dia. and composed of a nickel-steel alloy that doesn't occur naturally. Some have a thin shell about a quarter inch thick, when broken open are filled with a strange spongy material that disintegrates into dust upon contact with air. A complete mystery according to Roelf Marx curator of the South African Klerksdorp Museum, as the one he has on exibit rotates on its own, locked in a display case, free of outside vibrations. The manufactured metallic...