Grooved Sphere from South Africa (Precambrian)

Actually, it's a cricket ball.

Over the past several decades, South African miners have found hundreds of metallic spheres, at least one of which has three parallel grooves running around its equator. The spheres are of two types--"one of solid bluish metal with white flecks, and another which is a hollow ball filled with a white spongy center" (Jimison 1982). Roelf Marx, curator of the museum of Klerksdorp, South Africa, where some of the spheres are housed, said: "The spheres are a complete mystery. They look man-made, yet at the time in Earth's history when they came to rest in this rock no intelligent life existed. They're nothing like I have ever seen before" (Jimison 1982).