Interesting Septarian Free Form Sculptures are incredibly unusual.  Their color and formation are unlike any other stones - instantly recognizable. 

Septarian concretions or septarian nodules, are concretions containing angular cavities or cracks, called "septaria". The word comes from the Latinword septum; "partition", and refers to the cracks/separations in this kind of rock.  Descriptions dating from the 18th century attest to the fact that concretions have long been regarded as geological curiosities.