What is a pisolith in geology ?

Pisolith: definition

This term is used to designate mineral aggregates, generally carbonates or hydroxides of iron and aluminium, with a concentric structure, forming almost perfect spheres with a diameter greater than 2 mm. Below this size, we speak of oolite.

Photo : aragonite pisolites from Lamalou-les-Bains, Gard (30), France