Raman spectroscopy of selected borate minerals of the pinakiolite group

The Raman spectra of a series of related minerals of the pinakiolite group have been collected and the spectra related to the mineral structure. These minerals are based upon an isolated BO(3)(3-) ion. The site symmetry is reduced from D(3h) to C(1). Intense Raman bands are observed for the minerals takeuchiite, pinakiolite, fredrikssonite and azoproite at 1084, 1086, 1086 and 1086 cm(-1). These bands are assigned to the nu(1) BO(3)(3-) symmetric stretching mode. Low-intensity Raman bands are observed for the minerals at 1345, 1748; 1435, 1748; 1435, 1750; and 1436, 1749 cm(-1), respectively. One probable assignment is to nu(3) BO(3)(3-) antisymmetric stretching mode. Intense Raman bands of the studied minerals at 712 cm(-1) are attributed to the nu(2) out-of-plane bending mode. Importantly, through the comparison of the Raman spectra, the molecular structure of borate minerals with ill-defined structures can be obtained. Copyright (C) 2010 John Wiley & Sons, Ltd.