Klerksdorp Spheres are often classified as “Out-of-Place Artifacts”, a term coined by an American naturalist and cryptozoologist to indicate objects of historical, archaeological, or paleontological interest found in a very unusual or seemingly impossible context that could challenge conventional historical chronology by being "too advanced" for the level of civilization that existed at the time. These objects claim to provide evidences that suggest presence of intelligent beings well before humans were supposed to exist. Klerksdorp Spheres, however, aren’t out-of-place. Neither they are mysterious.
These spheres are actually concretion formed by the precipitation of volcanic sediments, ash, or both, after they accumulated 3 billion years ago. Concretions are often ovoid or spherical in shape because of which they are commonly mistaken to be dinosaur eggs, or extraterrestrial debris or human artifacts, in this case.
Examples of calcareous concretions, which exhibit equatorial grooves, found in Schoharie County, New York.
The latitudinal ridges and grooves exhibited by Klerksdorp Spheres are also natural and are known to occur in concretions found elsewhere on earth. Notable examples include "Moqui marbles" found within the Navajo Sandstone of southern Utah, and carbonate concretions found in Schoharie County, New York. Similar concretion as old as 2.8 billion years were also found in Hamersley Group of Australia.
Many false claims have been made regarding these objects. An often repeated claim is that testing by NASA found the spheres to be so precisely balanced that they could have only been made in zero-gravity. Not only there is no record of NASA ever saying that, the objects aren’t spherical at all as evident from these images. Another claim is that the spheres are manufactured of a metal "harder than steel", a statement which is rather meaningless as steel can vary in hardness depending on the type of alloy and treatment.
Specimens of Klerksdorp Spheres are housed in Klerksdorp Museum in Klerksdorp, a city about 70 km away from Ottosdal.
Moqui Marbles, hematite concretions, from the Navajo Sandstone of southeast Utah show similar grooves and shape.
Moeraki Boulders in New Zealand is another example of spherical concretion