A multimodal microcharacterization of trace-elements in defective pearls by SEM-CL, EPMA, µ-XRF and CONFOCAL RAMAN-IN-SEM imaging.

Guillaume Wille (1) , Xavier Bourrat (1) , Yannick Y. Lefrais (2) , Ute Schmidt (3)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 IRAMAT-CRP2A - IRAMAT-Centre de recherche en physique appliquée à l’archéologie
3 WITec

Pearls are greatly valued by the jewelry industry as shiny organic gems. Their glossiness, results of a defense mechanism against foreign particles. Pearls (Hyriopsis cumingii) are produced from a natural biomineralization process controlled by organic molecules. Pearl biocrystal is a hybrid composite: organic / mineral (3 % / 97 %). The regular form of pearl mineralization is aragonite, an orthorhombic polymorph of calcium carbonate. Each biocarbonate plateletis a polygranular composite of aragonite nanograinsstuck by proteins. It diffracts as a single crystal and is so called mesocrystal. Platelets have a polygonal shape, few hundreds of nanometersthick, whichstack along the c-axis with chitin organic 'cement'. This layered structure produces the well-known 'pearly' aspect. Sometimes, pearls show a biomineralization defect characterized by a lack of shine (also called 'milky pearl'). It has been established that this defect is related to the change in crystallization form: from orthorhombic aragonite to hexagonal vatérite [1]. Fig. 1: SEM observation of the interface: same area as seen with cathodoluminescence (CL, left) and in secondary electron mode (SE, right)

Mots clés: Elements; Perles; Metrologie

Domaines: Autre

Guillaume Wille, Xavier Bourrat, Yannick Y. Lefrais, Ute Schmidt. A multimodal microcharacterization of trace-elements in defective pearls by SEM-CL, EPMA, µ-XRF and CONFOCAL RAMAN-IN-SEM imaging.. EMAS 2017 15th European Workshop and IUMAS-7 Meeting, May 2017, Konstanz, Germany. ⟨hal-01491427⟩