Characterisation of the Copper Arsenate Mineral Strashimirite, Cu₈(AsO₄)₄(OH)₄·4H₂O, by near Infrared Spectroscopy

Abstract

Near infrared (NIR) spectra of the strashimirite minerals from two different origins have been investigated. The structure and spectral properties of a copper-bearing arsenate mineral are compared. Two prominent bands observed at 11,187 cm −1 and 8443 cm −1 (Czech) and 11327 cm −1 and 8732 cm −1 (Slovak) are assigned to 2 B 1g ® 2 B 2g and 2 B 1g ® 2 A 1g transitions of Cu 2+ ion in strashimirite. Intense bands at 7247 cm −1 and 6800 cm −1 are attributed to the first overtone of the water and OH fundamentals observed in a complex spectral profile centred upon 3300 cm −1. The very broad NIR band at 5150 cm −1 is assigned to combination bands of water and OH vibrations. Bands in the 4800 cm −1 to 4000 cm −1 are assigned to (AsO 4) 3− combination bands.

Near Infrared Spectroscopy of Selected Natural Magnesium Carbonates: Implications for Geosequestration

“…Carbonate bands are normally found in this spectral region resulting from the doubling of the symmetrical and antisymmetrical carbonate stretching bands 2(n 1 + n 3 ). [35][36][37] The NIR spectra of hydromagnesite and nesquehonite over the 5500-6200 cm -1 spectral range are illustrated in Figure 4. NIR bands for hydromagnesite are resolved at 5591 cm -1 , 5732 cm -1 and 5872 cm -1 , and for nesquehonite at 5593 cm -1 , 5718 cm -1 and 5882 cm -1 .…”

“…2n 1 ± dn). [35][36][37] The NIR spectra of hydromagnesite, dypingite and nesquehonite over the 7400-9000 cm -1 spectral range are shown in Figure 6. A broad spectral feature is noted, centred at around 8353-8391 cm -1 , together with some sharp bands at 7436 cm -1 , 7460 cm -1 , 7504 cm -1 , 7717 cm -1 , 7771 cm -1 , 7841 cm -1 , 7867 cm -1 and 7900 cm -1 for hydromagnesite, and at 7448 cm -1 , 7505 cm -1 and 7864 cm -1 for dypingite; and these bands are not observed for nesquehonite.…”