Ammonites, a pre-historic type of marine mollusc, had a vast existence of more than 300 million years. They from the Devonian period to the end of the Cretaceous system, when they became extinct around the same time as the dinosaurs. Now their history is stamped all over the earth in the form of some fascinating fossils casting the shells that these once squid-like creatures left behind.
Although most gemstones are mineral materials, a number of organic materials are also considered to be gemstones. The most common of these are pearl, bone (think opal fossils), amber, and ammonites. Ammonite fossils have been found on every continent, in all sorts of sizes and in lots of colors, though the most common naturally occurring colors for these fossils are brown and grey. Ammonite fossils form when ammonoids died and their shells became embedded in sand or silt. The shell was protected from damage over time due to the forming layers. As the layers formed and created pressure on the shell, mineral-rich water would seep into the chambers and eventually crystallize into the rock-like fossil we find today. Ammonite can sometimes end up with a rainbow-like sheen on the surface, opalized or pyritized.
It's no surprise that ammonites, with their spiral shape, are symbols of change and positive motion. The spiral draws in negative energy, filtering it through the chambers and releasing fresh, positive energy. Due to this connection with energy, ammonites have been used for activating Kundalini--the concept in Dharma that refers to primal energy (called shakti)--which coils at the base of the spine and is a source of life force or energy. Ammonites are associated with ancient knowledge, which makes sense considering how long these fossils have been around.