Raman spectroscopic study of the tellurite minerals: Graemite CuTeO3 H2O and teineite CuTeO3 2H2O

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae (a) A(XO3), (b) A(XO3).xH2O, (c) A2(XO3)3.xH2O, (d) A2(X2O5) and (e) A(X3O8). Raman spectroscopy has been used to study the tellurite minerals teineite and graemite; both contain water as an essential element of their stability. The tellurite ion should show a maximum of six bands. The free tellurite ion will have C3v symmetry and four modes, 2A1 and 2E. Raman bands for teineite at 739 and 778 cm-1 and for graemite at 768 and 793 cm-1 are assigned to the ν1 (TeO3)2- symmetric stretching mode whilst bands at 667 and 701 cm-1 for teineite and 676 and 708 cm-1 for graemite are attributed to the the ν3 (TeO3)2- antisymmetric stretching mode. The intense Raman band at 509 cm-1 for both teineite and graemite is assigned to the water librational mode. Raman bands for teineite at 318 and 347 cm-1 are assigned to the (TeO3)2- ν2 (A1) bending mode and the two bands for teineite at 384 and 458 cm-1 may be assigned to the (TeO3)2- ν4 (E) bending mode. Prominent Raman bands, observed at 2286, 2854, 3040 and 3495 cm-1, are attributed to OH stretching vibrations. The values for these OH stretching vibrations provide hydrogen bond distances of 2.550(6) Å (2341 cm-1), 2.610(3) Å (2796 cm-1) and 2.623(2) Å (2870 cm-1) which are comparatively short for secondary minerals