An SEM-EDX and Raman spectroscopic study of the fibrous arsenate mineral liskeardite and in comparison with other arsenates kaňkite, scorodite and yvonite

The mineral liskeardite, an arsenate mineral with major cations of iron and aluminium, has been studied by a combination of scanning electron microscopy with energy dispersive spectroscopy and Raman spectroscopy. The mineral shows a fibrous nature. Semi-quantitative chemical analysis shows an Al and Fe arsenate phase with minor amounts of K, Cu, S and Si. Scanning electron microscopy shows a fibrous material. Intense Raman bands at 893, 867 and 843 cm(-1) are assigned to the ν1 and ν3 AsO4(3)(-) and HOAsO3(2)(-) symmetric and antisymmetric stretching vibrations. Raman bands are observed at 514, 499, 485 and 477 cm(-1) and are assigned to the ν4 out of plane bending modes of the AsO4(3)(-) and HOAsO3(2)(-) units. The series of bands at 373, 356 and 343 cm(-1) are assigned to the ν2 symmetric bending modes. Two groups of OH stretching bands are observed and assigned to OH unit and water stretching vibrations. A comparison of the Raman spectrum of liskeardite with scorodite, kaňkite and yvonite is made.