8 x 2 x 8cm Septarian concretions are concretions containing cavities or cracks, called septaria. The septaria are the calcite (yellow) filled cracks at the center of the rock, indicating where the center of the concretions have shrunk, possibly during dehydration during its transformative journey over a long period of time. Septarian can be found mostly in the Gulf of Mexico and Madagascar. ***Due to natural variations in stones, appearance will vary***