Remember the metal ball that fell from the sky and landed in Namibia? That’s not the only mysterious spheres discovered in the southern Africa region. Klerksdorp Spheres, found in Ottosdal, South Africa, are round rocks that have intrigued those who find them.
By all scientific accounts, the rounded objects with even latitudinal grooves are 3 billion-year-old rocks that were naturally formed by carbonate concretions. Over the process of their development the tiny pyrophyllite spheres, which range in size from .5-10 cm, were created when minerals formed in the space between sediments. Weathering of these specimen left them as tiny balls, with evenly spaced lines circumscribing them.
Of course, this answer does not exactly satisfy those who believe the spheres are too perfect to have been created naturally, and since their first discovery in South African mines, they have been linked to intelligent beings from a different place or time.
Read more about Klerksdorp Spheres at Atlas Obscura. Link