Raman spectra of chillagite, wulfenite, stolzite, scheelite and wolframite were obtained at 298 and 77 K using a Raman microprobe in combination with a thermal stage. Chillagite is a solid solution of wulfenite and stolzite. The spectra of these molybdate minerals are orientation dependent. The band at 695 cm −1 is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The bands at 790 and 881 cm −1 are associated with the antisymmetric and symmetric A g modes of terminal WO 2 whereas the origin of the 806 cm −1 band remains unclear. The n 4 .E g / band was absent for scheelite. The bands at 353 and 401 cm −1 are assigned as either deformation modes or as r(B g ) and d.A g / modes of terminal WO 2 . The band at 462cm −1 has an equivalent band in the infrared at 455 cm −1 assigned as d as .A u / of the .W 2 O 4 / n chain. The band at 508 cm −1 is assigned as n sym .B g / of the .W 2 O 4 / n chain.
ABSTRACT. Intense weathering of copper orebodies in New South Wales and Queensland, Australia has produced an unusual suite of secondary copper minerals comprising chrysocolla, azurite, malachite and the phosphates libethenite and pseudomalachite. The phosphates persist in outcrop and show a marked zoning with libethenite confined to near-surface areas. Abundant chrysocolla is also found in these environments, but never replaces the two secondary phosphates or azurite. This leads to unusual assemblages of secondary copper minerals, that can, however, be explained by equilibrium models. Data from the literature are used to develop a comprehensive geochemical model that describes for the first time the origin and geochemical setting of this style of economically important mineralization.
The Raman and infrared spectra of vanadinite [Pb 5 (VO 4 ) 3 Cl] specimens from three localities were studied. Raman spectra were found to be both orientation and temperature dependent. Measurement of the Raman spectra at liquid nitrogen temperature allowed better band separation and increased the intensities of weak bands, thus permitting band assignment. Two types of isomorphous substitution were identified: (a) substitution in the bulk of the crystal where electron beam microanalysis identifies the presence of calcium and copper and (b) surface substitution where infrared spectroscopy shows the isomorphous substitution of vanadate by phosphate and of chloride by hydroxyl groups.
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