Septarian specimens are geodes that are a combination of yellow calcite, brown aragonite, grey limestone and white or clear barite. The word septarian comes from the Latin word "septum," meaning "partition." Septarian nodules contain angular cavities as a result of cracking, which are called septaria and create divisions throughout the stone. These unique septaria can be any length and each septarian can have many different cracks. Calcite leeches into the cracks of septarian to form calcite crystals on a layer of aragonite, which is on bentonite clay. Eventually, bentonite is replaced with limestone, resulting in the nodule turning to stone.
