Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and (to a lesser degree) the cylindrical baculite, Baculites compressus.
Ammonites were cephalopods, 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 ammonites died, they sank to the bottom and were buried by layers of bentonitic mud that eventually became shale.
Many gem-quality ammonites are found within siderite concretions.
These sediments preserved the aragonite of the shells, preventing it from converting to calcite.
Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and (to a lesser degree) the cylindrical baculite, Baculites compressus. Ammonites were cephalopods, 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 ammonites died, they sank to the bottom and were buried by layers of bentonitic mud that eventually became shale. Many gem-quality ammonites are found within siderite concretions. These sediments preserved the aragonite of the shells, preventing it from converting to calcite.
Ammolite