Raman microscopy of selected tungstate minerals

Abstract

A series of tungstate bearing minerals including scheelite, stolzite, ferberite, hübnerite, wolframite, russellite, tungstenian wulfenite and cuprotungstite have been analyzed by Raman microscopy. The results of the Raman spectroscopic analysis are compared with published data. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the pargenetic relationships between the minerals. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra. The ν1(Ag) band is observed at 909cm-1 and although the corresponding ν1(Bu) vibration should be inactive a minor band is observed around 894cm-1. The bands at 790 and 881cm-1 are associated with the antisymmetric and symmetric Ag modes of terminal WO2. The band at 695cm-1 is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The ν4(Eg) band was absent for scheelite. The bands at 353 and 401cm-1 are assigned as either deformation modes or as r(Bg) and δ(Ag) modes of terminal WO2. The band at 462cm-1 has an equivalent band in the infrared at 455cm-1 assigned as δas(Au) of the (W2O4)n chain. The band at 508cm-1 is assigned as νsym(Bg) of the (W2O 4)n chain. © 2003 Elsevier B.V. All rights reserved.