Structural characterization and chemical composition of aragonite and vaterite in freshwater cultured pearls

SOLDATI, ANALIA L.; JACOB, DORRIT E.; WEHRMEISTER, URSULA; HOFMEISTER, WOLFGANG

MINERALOGICAL MAGAZINE

Mineralogical Soc

Lugar: Middlesex; Año: 2008 vol. 72 p. 579 - 592

0026-461X

Vaterite and aragonite polymorphs in freshwater cultured pearls from mussels of the genus Hyriopsis (Unionidae) were structurally and compositionally characterized by Raman Spectroscopy, MicroComputer Tomography, high resolution Field Emission Scanning Electron Microscopy, Electron Probe Microanalyzer and Laser Ablation ICP-MS. The appearance of vaterite in pearls is related to the initial stages of the biomineralization, although we demonstrate that vaterite can not be a precursor of aragonite. It is not related to a particular crystal habit and therefore does not have a structural functionality in the pearls. Higher contents of elements typically bound to organic molecules, such as P and S in vaterite as well as higher total organic contents in vaterite as opposed to aragonite in concert with higher concentrations of Mn2+ and Mg2+ imply a stabilizing role of organic macromolecules and X2+ ions for biological vaterite. Distribution coefficients between aragonite and vaterite for provenance-independent elements, such as Mn and Mg (0.27 and 0.04, respectively) agree very well with those observed in fish otoliths.