Through tectonic pressure and mineralization, marine mollusks that lived 71 million years ago beneath the Bearpaw Sea have been fossilized. These fossils have revealed the only species of Ammonites that produce gem-quality Ammolite. The gem material is formed by the compression of prehistoric Ammonites in shale layers, resulting in perfectly preserved fossils.

While ammonite species have been discovered globally, only Placenticeras meeki, Placenticeras intercalare, and Baculites compressus fossils exhibit a range of iridescent rainbow colors.