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

ABSTRACT

Gilalite is a copper silicate mineral with a general formula of Cu₅Si₆O₁₇ · 7H₂O. The mineral is often found in association with another copper silicate mineral, apachite, Cu₉Si₁₀O₂₉ · 11H₂O. 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 1160 cm⁻¹.

The Raman band at 853 cm⁻¹ is assigned to the –SiO₃ symmetrical stretching vibration and the low-intensity Raman bands at 914, 953, and 964 cm⁻¹ may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman band at 673 cm⁻¹ with a shoulder at 663 cm⁻¹ is assigned to the ν₄ Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.