Klerksdorp spheres
Links:
https://www.lehigh.edu/~x010/klerksdorp.html
https://en.wikipedia.org/wiki/Klerksdorp_sphere
https://ncse.ngo/mysterious-spheres-ottosdal-south-africa
https://archive.org/stream/pdfy-LN0OpY4ng1hKOfR7/Michael+A.+Cremo+Richard+l.+Thompson+-+The+Hidden+History+of+the+Human+Race+1998_djvu.txt