Iridescent Ammonite

A very large iridescent ammonite from the Late Cretaceous period from Alberta, Canada, made its way to the Smithsonian Museum of Natural History. The 71 million years old extinct shelled marine animal which is related to the octopus and the squid, is resplendent in iridescent shades of red, blue, orange, and green colors. The colored iridescence is caused by the reflection of light from layers of aragonite that make up the shell of the ammonite. These ammonite shells resemble hues and characteristics of opal and are mined today, cut, polished, and sold under the gemstone name of “ammolite.”

How are ammonites mined? In the KORITE mine in Alberta, ammonite fossils are found randomly in layers of shale. Once spotted in a compressed shale, the ammonite is stabilized in situ, the first step in excavation. Ammonite fossils are so fragile that, without stabilizing glue, the fossils would shatter. The whole site is impregnated with glue. After the glue dries, the fossil is removed by digging trenches with picks and hammers around it, usually leaving 5 cm around the precious discovery. The digging underneath the fossil and the stress usually causes the rock around it to cleave, thus releasing the precious fossil. The fossil is then carried to Calgary for further processing into precious stones used in jewelry.