Welcome to our Septarian Concretion page!

Septarians were formed approximately 110 million years ago when the Gulf of Mexico reached what is now southern Utah. Decomposing sea (shell) life, killed by volcanic actions had a chemical attraction for the sediment around them, forming mud balls. Tide and wave action rolled the balls around, increasing the size of many of them. As the ocean retreated, the balls were left to dry and crack. Because of their bentonite content, they also shrank, trapping the cracks inside. They were then covered with sediment. The ocean returned, depositing shell life above the balls. As this decomposed, calcite from the shells was carried down into the cracks, and calcite crystals formed. A thin wall of calcite was transformed into aragonite, dividing the clay exteriors from the calcite centers. Because of this, the geodes are called Septarians. (septum in Latin) They fluoresce nicely under black, or u-v lamps!

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