Pyritized Ammonites are considered some of the most collectable type of Ammonite fossil specimens. Iron Pyrite, also known as "Fool's Gold" enters the Ammonites chambers, replacing the animal's structure cell by cell. When the cellular replacement process goes just right, a magnificent fossil specimen such as the one pictured is created. The name Pyrite is derived from the Greek πυρίτης (puritēs), "of fire" or "in fire," from πύρ (pur), "fire.”
Ammonites are an extinct group of marine animals in the Cephalopoda class. They are invertebrates and are more closely related to coleoids (squids, octopus, and cuttlefish) than they were to the chambered nautilus, even though they looked much more similar to the later. The name Ammonite was derived from "ammonis cornua," translated to mean Horns of Ammon. Ammon was an Egyptian god that was typically depicted wearing ram horns, whose spiraled shape is similar to that of an Ammonite. Ammonites first appeared in the oceans during the Devonian Period, some 400 million years ago. They died out around 65.5 million years ago along with the dinosaurs.