Formation mechanism of CaCO3 spherulites in myostracum layer of limpet sahells

Abstract

CaCO3 spherulites were found in the myostracum layer of common limpet shells collected from East Sands, St Andrews, Scotland. Their microstructures were revealed by using powder X- ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, and energy dispersive X-ray microanalysis. The formation mechanisms of these spherulites and their morphology evolution were postulated. It was proposed that spherical particles of an inorganic and biological composite formed first. In the centre of each spherical particle was developed a double-layer disk of vaterite crystal sandwiching a biological sheet. The disk crystal supplies a relatively strong mirror symmetric dipole filed, guiding the orientations of the nanocrystallites and the arrangement of mesorods, and therefore, determining the final morphology of the spherulite.