Infrared and Raman Spectroscopic Characterization of the Silicate Mineral Gilalite Cu5Si6O17•7H2O

Gilalite is a copper silicate mineral with a general formula of Cu5Si6O17 center dot 7H(2)O. The mineral is often found in association with another copper silicate mineral, apachite, Cu9Si10O29 center dot 11H(2)O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman bands are observed at 1066, 1083, and 1160cm(-1). The Raman band at 853cm(-1) is assigned to the -SiO3 symmetrical stretching vibration and the low-intensity Raman bands at 914, 953, and 964cm(-1) may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman band at 673cm(-1) with a shoulder at 663cm(-1) is assigned to the nu(4) Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.