This formation looks as if it was created by a huge, heavy object dropping on the middle of it and splintering it. It's what a piece of glass would look like if a rock were to fall on it.
However, according to the way I understand rock is formed, it's more likely that it used to be a mound of compacted mud which sank and split as the water seeped out and evaporated from it. It looks like it's sitting in a shallow well.
Moss can grow on rock because it doesn't have any actual roots. It has filament-like rhizomes which can just spread out on top of the rock and absorb moisture from its surface.
