Near Infrared Spectroscopy of Aurichalcite (Zn,Cu2+)5(CO3)2(OH)6

In this endeavour near-infrared spectroscopy studies show an evidence for variable composition in aurichalcite minerals of zinc copper carbonate hydroxides. The observation of a broad feature in the electronic part of the spectrum around 11500 cm-1 (0.87 µm) is a strong indication of Cu2+ substitution for Zn2+ in the mineral. Overtones of OH vibrations in the spectra from 7250 to 5400 cm-1 (1.38 to 1.85µm) show strong hydrogen bonding in these carbonates. A band common to spectra of all carbonates appears near 5400 cm-1 (1.85 µm) due to the combination of both OH-stretching and HOH-bending vibrations, may be attributed to adsorbed water by the minerals. Aurichalcite minerals display a spectral sequence of five absorpton bands with variation of both band positions and intenities and this is the chief spectral feature observed in the range 5200 -5100 cm-1 (1.92 - 2.38 µm) due to vibrational processes of the carbonate ion. The frequency shifts of carbonate bands suggest the effect of divalent cations and or variations of Zn/Cu ratio in aurichalcite minerals