Base-Cut Septarian

From the Henry Mountains of Utah, the mineral Septarian formed in an ancient sea floor some 50-70 million years ago as sediment collected around sea life as they decomposed. Calcium carbonate from the shells of these creatures began to take a new form over time, creating calcite crystals and bands of aragonite. The gold colored crystals inside is calcite, the brown is aragonite, and the outer surface is composed of limestone.