An application of near-infrared and mid-infrared spectroscopy to the study of selected tellurite minerals: xocomecatlite, tlapallite and rodalquilarite

Abstract

Near-infrared and mid-infrared spectra of three tellurite minerals have been investigated. The structure and spectral properties of two copper bearing xocomecatlite and tlapallite are compared with an iron bearing rodalquilarite mineral. Two prominent bands observed at 9855 and 9015 cm-1 are assigned to 2B1g ® 2B2g and 2B1g ® 2A1g transitions of Cu2+ ion in xocomecatlite. The cause of spectral distortion is the result of many cations of Ca, Pb, Cu and Zn the in tlapallite mineral structure. Rodalquilarite is characterised by ferric ion absorption in the range 12300-8800 cm-1. Three water vibrational overtones are observed in xocomecatlite at 7140, 7075 and 6935 cm-1 where as in tlapallite bands are shifted to low wavenumbers at 7135, 7080 and 6830 cm-1. The complexity of rodalquilarite spectrum increases with more number of overlapping bands in the near-infrared. The observation of intense absorption feature near 7200 cm-1 confirms strongly hydrogen bonding water molecules in xocomecatlite. Weak bands observed near 6375 and 6130 cm-1 in tellurites are attributed to the hydrogen bonding between (TeO3)2- and H2O. A number of overlapping bands in the low wave numbers 4800-4000 cm-1 are caused by combinational modes of tellurite ion. (TeO3)2-stretching vibrations are characterized by three main absorptions at ~ 1070, 780 and 665 cm-1.