Polarized mapping Raman spectroscopy: identification of particle orientation in biominerals

Abstract

Abstract The identification of the texture of biominerals and the particle orientation in the bivalve shells of Anodonta cygnea was performed using polarized Raman spectroscopy mapping measurements. A single crystal of aragonite served as a reference to disclose orientational information on the mesoscopic scale. The relative intensities of different Raman modes combined with the determination of depolarization ratio of the Ag Raman mode at 1087 cm−1 of an aragonite single crystal was used to indicate the angular variation of aragonite crystallites in biominerals. The imaging technique shows that the a- and b-axis of aragonite crystallites in both, nacreous and prismatic layers do not only have one orientation but they are organized in a domain-type arrangement. The angular divergence in the prismatic layer of the shells is larger and hence, the crystallites in the nacreous layer have a higher degree of co-orientation. Results provide relevant textural information about aragonitic shells and indicate a sensitive technique to evaluate the crystal orientation in biominerals.