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 2B1g→2B2g and 2B1g→2A1g transitions of Cu2+ 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 (AsO4)3− combination bands.