Micro-Raman spectroscopy of selected Mo minerals from Su Seinargiu (Sardinia, Italy)

Abstract

Raman spectra of selected molybdenum minerals, represented both by bismuth-molybdenum oxides (sardignaite, gelosaite, and mambertiite) and by molybdates [tancaite-(Ce), ichnusaite, nuragheite, and suseinargiuite] from the Su Seinargiu Mo-Bi prospect (Sardinia, Italy) are reported. Raman spectra were collected using samples previously characterized through X-ray diffraction and electron-microprobe analyses. Bismuth-molybdenum oxides are mainly characterized by bands in the range between 300 and 1000 cm^-1, related to stretching modes of Mo–O and to Bi–O bonds. Broad bands related to O–H stretching modes were observed in the range between 3000 and 4000 cm^-1. Raman spectra of molybdates are characterized by the four fundamental modes of MoO₄ groups occurring between 250 and 1000 cm^-1. Additionally, bending and stretching bands related to O–H bonds were observed. Micro-Raman spectroscopy may usually be an efficient tool for the discrimination of these rare phases, with some exceptions discussed in the text.