Molecular Structure of the Adelite Group of Minerals - A Raman Spectroscopic Study

The application of Raman microscopy to the study of closely related mineral phases of the adelite group has enabled their molecular characterisation. The adelite group of minerals are orthorhombic arsenates and vanadates of general formula AB2+(XO4)(OH) where X may be As5+ or V5+ and cation A may be Ca or Pb; cation B may be Co or Cu and others. Raman spectroscopy has proven most powerful for the identification of these minerals. In particular the position of the hydroxyl stretching vibrations and most of the arsenate bands have been identified. The two minerals tangeite and calciovolborthite have previously been identified as the same mineral. Raman spectroscopy has proven that the minerals are not identical and have different structures. The application of Raman spectroscopy to the study of these minerals shows that increased distortion of the arsenate anion occur as the cationic substitution from conichalcite to austinite to duftite occurs.