Roelf Marx: "There is nothing scientific published about the globes, but the facts are: They are found in pyrophyllite, which is mined near the little town of Ottosdal in the Western Transvaal. This pyrophyllite (Al2Si4O10(OH)2) is a quite soft secondary mineral with a count of only 3 on the Mohs' scale and was formed by sedimentation about 2.8 billion years ago. On the other hand the globes, which have a fibrous structure on the inside with a shell around it, are very hard and cannot be scratched, even by steel."
"It also seems that the spheres are so delicately balanced that, even with modern technology, they would need to have been made in zero gravity. The story goes that scientists at NASA were totally flawed when they examined them, and were unable to come up with any explanation." However some of the photographs do not seem to support this.