Horn Coral grows in long cone shapes and are formed from the calcium carbonate that came from the ocean floor. They are estimated to be between 251 and 488 million years old! The proper name for these fossils is Rugose Coral. This fossil is regarded as a soothing and protective stone. This stone and fossils in general are said to help you tap into ancient wisdom when learning a new spiritual tradition. This fossil is commonly found along the shores of the Great Lakes.