The role of organic pigments in biogenic and synthetic calcite lattice distortions

The wide range of color observed in skeletal elements of marine calcifying invertebrates, in particular, in sea urchin biominerals, is due to the presence of a family of organic pigment molecules: the polyhydroxylated naphthoquinones (PHNQ), which are incorporated within the biominerals. It is well known that intra-crystalline organic molecules induce lattice distortions within the biogenic crystals as compared to geological ones and participate in shaping the complex morphologies of biominerals. However, the specific role of the organic pigments on the resulting biomineral lattice distortions has never been investigated to our knowledge. Here, we aim to do so by performing high-resolution X-ray powder diffraction (HR-XRPD) measurements at ID22 of sea urchin spines of different colors and of synthetic CaCO3 samples colored by PHNQ molecules.