These nodules grow around a nucleus of sharks tooth, or simular, and are very layered. they grow in the very upper layers of the sediment bed, and are kept, in theory, on top of this bed, by bioturbitation. That is things such as crabs, and holothurians.
(i wonder what keeps all the mars berries on top of the soil?)
The slow moving currents, bring the minerials for growth.
These mag nodules are not anywhere near as round as mars berries.
So, shape? Growth rings? core?
I learned a new word, bioturbidation.
Maybe, the core of the mars berries are Round, to start with?
