AMMONITE

Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meek and Placenticeras intercalate, and (to a lesser degree) the cylindrical baculite Baculites compressus. Ammonites were cephalopods, or squid-like creatures, that thrived in tropical seas until becoming extinct along with the dinosaurs at the end of the Mesozoic era.

The ammonites that form Ammolite inhabited a prehistoric, inland subtropical sea that bordered the Rocky Mountains—this area is known today as the Cretaceous or Western Interior Seaway. As the seas receded, the ammonites were buried and crushed by layers of bentonite sediment.

This sediment preserved the aragonite of their shelled remains, preventing it from converting to calcite. Through diagenesis, the shells were impregnated by trace elements present in these sediments, the most common of these being iron and copper, this accounts for the predominance of the red & green colours. Mechanized mining operations are fairly basic, involving the excavation of shallow pits with backhoes.

Significant deposits of gem-quality ammolite are only found in the Bearpaw Sea formation that extends from Alberta to Saskatchewan in Canada and south to Montana in the USA. The best grade of gem quality Ammolite is along high energy river systems on the eastern slopes of the Rockies in southern Alberta.