The sheer magniture of this place proves this title -- there are THOUSAND of such concretions, all quite dense

Many touristic blogs tell, that their origin is unclear, but there already is a good theory on their formation

For a core lays an organic material (like shells or bones) inside a fossil

This fossil attaches more and more minerals like calcite; and with fossil withering the sphere the sphere opens for the world to see

In general, those are two- or even multilayered spheres with a core