title: A vibrational spectroscopic study of the phosphate mineral zanazziite - Ca₂(MgFe²+)(MgFe²+Al)₄Be₄(PO₄)6.6(H₂O).
abstract: Zanazziite is the magnesium member of a complex beryllium calcium phosphate mineral group named roscherite. The studied samples were collected from the Ponte do Piauí mine, located in Itinga, Minas Gerais. The mineral was studied by electron microprobe, Raman and infrared spectroscopy. The chemical formula can be expressed as Ca(2.00)(Mg(3.15),Fe(0.78),Mn(0.16),Zn(0.01),Al(0.26),Ca(0.14))Be(4.00)(PO(4))(6.09)(OH)(4.00)⋅5.69(H(2)O) and shows an intermediate member of the zanazziite-greinfeinstenite series, with predominance of zanazziite member. The molecular structure of the mineral zanazziite has been determined using a combination of Raman and infrared spectroscopy. A very intense Raman band at 970 cm(-1) is assigned to the phosphate symmetric stretching mode whilst the Raman bands at 1007, 1047, 1064 and 1096 cm(-1) are attributed to the phosphate antisymmetric stretching mode. The infrared spectrum is broad and the antisymmetric stretching bands are prominent. Raman bands at 559, 568, 589 cm(-1) are assigned to the ν(4) out of plane bending modes of the PO(4) and HPO(4) units. The observation of multiple bands supports the concept that the symmetry of the phosphate unit in the zanazziite structure is reduced in symmetry. Raman bands at 3437 and 3447 cm(-1) are attributed to the OH stretching vibrations; Raman bands at 3098 and 3256 are attributed to water stretching vibrations. The width and complexity of the infrared spectral profile in contrast to the well resolved Raman spectra, proves that the pegmatitic phosphates are better studied with Raman spectroscopy.
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia. r.frost@qut.edu.au
authors.forename: Ray L
authors.initials: RL
authors.lastname: Frost
authors.forename: Yunfei
authors.initials: Y
authors.lastname: Xi
authors.forename: Ricardo
authors.initials: R
authors.lastname: Scholz
authors.forename: Fernanda M
authors.initials: FM
authors.lastname: Belotti
authors.forename: Luiz Alberto
authors.initials: LA
authors.lastname: Dias Menezes Filho
mesh_terms: D001938:Brazil; D008670:Metals / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D014732:Vibration
chemical_list: D008670:Metals; D008903:Minerals; D010710:Phosphates