Mohs Hardness of 3.5-5 with a trigonal crystal structure (of the outer layer)
Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian period (over 400 million years ago) and became extinct at the close of the Cretaceous period, along with the dinosaurs.
The classification of ammonoids is based in part on the ornamentation and structure of the septa comprising their shells’ gas chambers; by these and other characteristics subclass Ammonoidea is divided into three orders and eight known suborders. While nearly all nautiloids show gently curving sutures, the ammonoid suture line (the intersection of the septum with the outer shell) was folded, forming saddles/peaks and lobes/valleys.
Ammolites (going by the trade name Korite) are thin, iridescent layers of the ammonites fossilized shell. The Ammonites that become Ammolite lived primarily in an inland subtropical sea referred to now as the Western Interior Seaway, just east of the Rocky Mountains near Alberta Canada. Near the end of the Mesozoic era this sea receded, and all of the Ammonites died away. The remnants of the shells were eventually covered by volcanic ash and other sediments brought to the sea from rivers off the mountains. Pressed by these sediments (called Bentonite) the fossils were preserved and eventually became coated an morphed into the Ammolite. The iridescence of Ammolite is determined by the thicknesses of the crystallized layering and the resulting intensity of light diffraction.X