These ammonites lived on this planet during the Cretaceous period, and to be specific, about 65 to 240 million years ago. Although you can find these fossils around different parts of the world, the ones found in the Rocky Mountains of North America are the most fit for making ammolite jewelry such as ammolite rings, ammolite earrings, ammolite pendants, and ammolite bracelets. Ammolite stone is used by various jewelers to make some of the finest gemstone jewelry.