One of the Wonderstone (Ottosdal or Klerksdorp) spheres.
In the Wonderstone Mines at Ottosdal (West Transvaal, South Africa), hundreds of metallic spheres have been found over several decades in pyrophillite (or wonderstone) deposits of Precambrian date, some 2.8 billion years old.
Pyrophillite is a metamorphosed sedimentary mineral mined for use in masonry buildings, as an absorbent, as a filler, as an ingredient in industrial compounds and for a variety of other uses. Two types of sphere are alleged to have been found in the pyrophillite; one is a bluish metal with white inclusions, while the other has a metallic coating around a spongy material.
Only examples of the second type seem to have been examined by geologists, who have found that they consist of pyrites and goethite. At least one of these spheres has three parallel fine grooves running around its center. Lab technicians were said to be at a loss to explain how they could have been formed by any known natural process…
See web page
showme.co.za/tourism/the-klerksdorp-museum-mine-tours-klerksdorp/