Septarian Bookends, Utah

These strange and handsome Geodes are from the Henry Mountains of Utah. Originally formed in an ancient sea floor some 50-70 million years ago, sediment collected around sea life as they decomposed, forming a concretion. Calcium carbonate from the shells of these creatures began to take a new form over time, creating calcite crystals and bands of aragonite. As the oceans receded, these mud balls hardened, shrinking and cracking in the sun. The gold colored crystals inside are the calcite, the brown is aragonite, and the outer surface is composed of limestone.