Brilliant structural colors originating from reflection by nanogaps of nacreous layers in fossilized ammonite shells

Abstract

Abstract Vivid-colored ammonite fossils that are mined in Alberta, Canada, are known as gemstones called “Ammolite.” The specific colors having narrow reflectance spectra are ascribed to an interference phenomenon on the preserved nacre of fossils. However, the essence of the vivid tones that are different from the structural coloration of other kinds of shells has not been revealed. In this work, we clarified that specific reflection by interlaminar nanogaps (~ 4 nm) of aragonite plates with the homogeneous lamination period in the fossilized nacreous layers is essential for the emergence of vivid structural colors depending on the thickness of the layer.