Nodule (geology)

Normally, a nodule has a warty or knobby surface and exists as a discrete mass within the host strata.

In general, they lack any internal structure except for the preserved remnants of original bedding or fossils.

Minerals that typically form nodules include calcite, chert, apatite (phosphorite), anhydrite, and pyrite.

[1][2] Nodular is used to describe a sediment or sedimentary rock composed of scattered to loosely packed nodules in matrix of like or unlike character.

[1] Nodule is also used for widely scattered concretionary lumps of manganese, cobalt, iron, and nickel found on the floors of the world's oceans.