Vibrational spectroscopic study of the copper silicate mineral ajoite (K,Na)Cu7AlSi9O24(OH)6•3H2O

Ajoite (K,Na)Cu7AlSi9O24(OH)(6)center dot 3H(2)O is a mineral named after the Ajo district of Arizona. Raman and infrared spectroscopy were used to characterise the molecular structure of ajoite. The structure of the mineral shows disorder which is reflected in the difficulty of obtaining quality Raman spectra. The Raman spectrum is characterised by a broad spectral profile with a band at 1048 cm(-1) assigned to the v(1) (A(1g)) symmetric stretching vibration. Strong bands at 962, 1015 and 1139 cm(-1) are assigned to the v(3) SiO4 antisymmetric stretching vibrations. Multiple v(4) SiO4 vibrational modes indicate strong distortion of the SiO4 tetrahedra. Multiple AlO and CuO stretching bands are observed. Raman spectroscopy and confirmed by infrared spectroscopy clearly shows that hydroxyl units are involved in the ajoite structure. Based upon the infrared spectra, water is involved in the ajoite structure, probably as zeolitic water. (C) 2011 Elsevier B.V. All rights reserved.