Phylum Mollusca, Class Cephalopoda, Subclass Ammonoidea, Order Ammonitida
Geological Time: Upper Cretaceous
Size: 50 mm
Fossil Site: Fox Hills Formation, North Dakota
This is a truly remarkable specimen of this Cretaceous ammonite. While diminutive, the specimen exhibits as much opalescence as I have ever seen. A greenish-blue dominates the spectrum, with a good dose of purple.
Also see: Ammonite Fossils
click to enlarge