Ammonites & Rainbow Pyrite Nodule Composite

Ammonite info - Quenstedtoceras Callovian, Middle Jurassic  Moscow Basin 4x3.5x3" Iridescent ammonite fossils are extraordinary remnants of ancient marine cephalopods, displaying a captivating, rainbow-like shimmer. This iridescence arises from the preservation of the shell’s original microstructure, which diffracts light. Beyond their visual appeal, these fossils hold scientific importance, offering insights into the environmental conditions under which they formed and were preserved. Ammonites, including those with iridescent shells, had a planispiral shell, meaning it coiled in a single plane. This spiral structure featured multiple whorls—each a complete 360-degree turn of the shell. Composed primarily of aragonite, a crystalline form of calcium carbonate, ammonite shells sometimes retained their original composition, enabling the iridescent effect seen in fossils. The iridescence results from the preservation of the nacreous (mother-of-pearl) layer, which consists of microscopic,