Iridescent ammonites are fossilised shells of the extinct group of marine animals ammonites, which lived during the Mesozoic Era, between 240 - 65 million years ago. Ammonites were closely related to modern-day cephalopods such as squid, octopi, and nautili, but they had a distinctive coiled shell that could grow to more than two meters in diameter.

Iridescent ammonite's remarkable shell surface is created by a combination of structural and chemical properties, which reflect light in unique ways. The iridescence of ammonites is caused by light waves being scattered and refracted by the microscopic structure of the shell material. The shell is made up of layers of aragonite, a mineral that has a unique crystal structure that reflects light. As light waves pass through these layers, they interfere with each other, creating a spectrum of colours that change depending on the angle of the light source and the observer. The rarest and most sought-after colour found in these fossils is the deep shape of ultramarine, a colour sought after by fossil collectors across the globe.

The colours found in our specimens are caused by the combination of millions of years of compression and the mineralisation of iron, copper and silica which precipitated from volcanic ash. Ammolite is found primarily in the Rocky Mountains of North America, and it is only mined in a few locations in Canada. 

In October 2020, the record price for this collectable fossil was set at Christie’s ‘Sculpted By Nature’ sale, where a large ammonite sold for £325,000 - far exceeding its estimate of £60,000 - £90,000.