Septarian concretions or septarian nodules, are concretions containing angular cavities or cracks, called "septaria". The word comes from the Latin word septum; "partition", and refers to the cracks/separations in this kind of rock.[2] Some websites incorrectly derive the term from the Latin word septem, meaning "seven".[3] Cracks are highly variable in shape and volume, as well as the degree of shrinkage they indicate.