This type of geode is sedimentary, which formed in an ancient sea floor about 50 million years ago. This is different from most geodes which are volcanic in nature. The septarian geode's golden star-like centers are the result of the crystallization of the mineral calcite, framed by aragonite. Some are filled in completely with calcite, while others left hollows showing the tooth-like calcite crystals and in rare cases, some perfect crystals of barite as well. Septarians are found almost exclusively in Utah.