This is one exceptional cabochon, made of agatized Colus. The Colus were ancient sea creatures that dwelled in shells like today's snails. Over time, they were slowly replaced by agate, forming the lovely fossil samples we see today. This sample has several - the lighter areas in the photos are clearly translucent agate. The large central Colus is set off by a brown/gold colored shell, and just adds to the beauty of this stone.