Disordered dolomite as an unusual biomineralization product found in the center of a natural Cassis pearl

Natural pearls are produced without human intervention, mainly due to various irritations from the surrounding environment to their mantle tissues. Pearls usually possess similar mineral compositions to the host shells, which means they are also dominated by aragonite and calcite. In this study, we report a natural pearl from a Cassis species mollusk containing granular central structures. Raman spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), energy dispersive X-ray spectroscopy (EDS) coupled with scanning electron microscope (SEM), and X-ray diffraction (XRD) analyses were carried out in order to characterize the mineral composition in the center region of this pearl. Our results showed that this pearl’s center was made of mostly disordered dolomite (Ca(0.53)Mg(0.47)CO(3)) mixing with small amount of aragonite and high magnesium-calcite. To the best of our knowledge, this is the first time disordered dolomite was conclusively identified inside of a natural pearl and such information expanded our knowledge on internal growth structures and formation of natural pearls.