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

Near-infrared and mid-infrared spectra of three tellurite minerals have been investigated. The structures and spectral properties of copper bearing xocomecatlite and tlapallite are compared with an iron bearing rodalquilarite mineral. Two prominent bands observed at 9,855 and 9,015 cm⁻¹ are assigned to ²B_1g → ²B_2g and ²B_1g → ²A_1g transitions of Cu²⁺ ion in xocomecatlite. The cause of spectral distortion is the result of many cations of Ca, Pb, Cu and Zn in the tlapallite mineral structure. Rodalquilarite is characterised by ferric ion absorption in the range 12,300–8,800 cm⁻¹. Three water vibrational overtones are observed in xocomecatlite at 7,140, 7,075 and 6,935 cm⁻¹ whereas in tlapallite bands are shifted to lower wavenumbers at 7,135, 7,080 and 6,830 cm⁻¹. The complexity of rodalquilarite spectrum increases with the number of overlapping bands in the near-infrared. The observation of intense absorption feature near 7,200 cm⁻¹ confirms hydrogen bonding water molecules in xocomecatlite. Weak bands observed near 6,375 and 6,130 cm⁻¹ in tellurites are attributed to the hydrogen bonding between (TeO₃)²⁻ and H₂O. A number of overlapping bands at low wave numbers 4,800–4,000 cm⁻¹ are caused by combinational modes of tellurite ion. (TeO₃)²⁻ stretching vibrations are characterised by three main absorptions at ~1,070, 780 and 665 cm⁻¹. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.