Ammolite: Iridescent Ammonite Fossil

Ammonites that display an iridescence are called ammolites. The stunning rainbow color is the result of nacre (mother of pearl), which is the substance that made up the animal's shell. This then fossilized and became a mineral known as aragonite.

The colors result from light reflecting off of layers within the fossilized shell and interacting, much the way oil on water produces a rainbow sheen. Ammolite is one of only three gemstones produced by living organisms, along with amber and pearls.

Ammonites have been collected and prized for their geometrical beauty for many thousands of years.

Ammonites became extinct at the end of the Cretaceous Period some 65 million years ago after a 330 million year survival on earth.

Matched ammonite pair

Named for Ammon, the Egyptian god of Procreation and Life, these ancient marine mollusks (cephalopods) were similar to the modern squid, octopus and nautiloids. They were creatures of the open tropical seas and are abundant in limestones from tropical reefs. These were perhaps the most agile and intelligent of the invertebrate carnivores, living in ocean waters of all depths.

The characteristic spiral was formed by partitions or chambers of the coiled shell where they lived. Once the ammonite grew too large for its living chamber, it formed a new one and moved into it. The empty chambers filled with gas to assist buoyancy at different depths in the oceans.

Ammonites have been collected and prized for their geometrical beauty for many thousands of years.

Ammonites became extinct at the end of the Cretaceous Period some 65 million years ago after a 330 million year survival on earth. [5]