Utah Septarian Nodules

Septarians were formed millions of years ago when the Gulf of Mexico reached what is now Southern Utah. Decomposing sea life, killed by volcanic eruptions had a chemical attraction for sediment around them, forming mud balls. As the ocean receded the balls were left to dry and crack. Because of their bentonite content they also shrank at the same time trapping the cracks inside. As decomposed calcite from the hells was carried down into the cracks in the mud ball, calcite crystals formed.