title: A Raman and infrared spectroscopic analysis of the phosphate mineral wardite NaAl3(PO4)2(OH)4⋅2(H2O) from Brazil.
abstract: A wardite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been examined by vibrational spectroscopy. The mineral is unusual in that it belongs to a unique symmetry class, namely the tetragonal-trapezohedral group. The structure of wardite contains layers of corner-linked -OH bridged MO6 octahedra stacked along the tetragonal C-axis in a four-layer sequence and linked by PO4 groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 995 and 1051cm(-1) are assigned to the ν1PO4(3-) symmetric stretching mode. Intense Raman bands are observed at 605 and 618cm(-1) with shoulders at 578 and 589cm(-1) are assigned to the ν4 out of plane bending modes of the PO4(3-). The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Sharp infrared bands are observed at 3544 and 3611cm(-1) are attributed to the OH stretching vibrations of the hydroxyl units. Vibrational spectroscopy enables subtle details of the molecular structure of wardite to be determined.
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia. Electronic address: r.frost@qut.edu.au.
authors.forename: Ray L
authors.initials: RL
authors.lastname: Frost
authors.affiliation: Geology Department, School of Mines, Federal University of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto, MG 35400-00, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Scholz
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
authors.forename: Andrés
authors.initials: A
authors.lastname: López
authors.affiliation: Geology Department, School of Mines, Federal University of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto, MG 35400-00, Brazil.
authors.forename: Cristiano
authors.initials: C
authors.lastname: Lana
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
authors.forename: Yunfei
authors.initials: Y
authors.lastname: Xi
mesh_terms: D017665:Hydroxyl Radical / Q000032:analysis; D008903:Minerals / Q000737:chemistry*; D010710:Phosphates / Q000032:analysis; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
chemical_list: D008903:Minerals; D010710:Phosphates; D017665:Hydroxyl Radical
keywords: Cyrilovite; Hydroxyl; Phosphate; Raman spectroscopy; Wardite