title: A study of the phosphate mineral kapundaite NaCa(Fe3+)4(PO4)4(OH)3⋅5(H2O) using SEM/EDX and vibrational spectroscopic methods.
abstract: Vibrational spectroscopy enables subtle details of the molecular structure of kapundaite to be determined. Single crystals of a pure phase from a Brazilian pegmatite were used. Kapundaite is the Fe(3+) member of the wardite group. The infrared and Raman spectroscopy were applied to compare the structure of kapundaite with wardite. The Raman spectrum of kapundaite in the 800-1400 cm(-1) spectral range shows two intense bands at 1089 and 1114 cm(-1) assigned to the ν1PO4(3-) symmetric stretching vibrations. The observation of two bands provides evidence for the non-equivalence of the phosphate units in the kapundaite structure. The infrared spectrum of kapundaite in the 500-1300 cm(-1) shows much greater complexity than the Raman spectrum. Strong infrared bands are found at 966, 1003 and 1036 cm(-1) and are attributed to the ν1PO4(3-) symmetric stretching mode and ν3PO4(3-) antisymmetric stretching mode. Raman bands in the ν4 out of plane bending modes of the PO4(3-) unit support the concept of non-equivalent phosphate units in the kapundaite structure. In the 2600-3800 cm(-1) spectral range, Raman bands for kapundaite are found at 2905, 3151, 3311, 3449 and 3530 cm(-1). These bands are broad and are assigned to OH stretching vibrations. Broad infrared bands are also found at 2904, 3105, 3307, 3453 and 3523 cm(-1) and are attributed to water. Raman spectroscopy complimented with infrared spectroscopy has enabled aspects of the structure of kapundaite to be ascertained and compared with that of other phosphate minerals.
authors: 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: Ray L
authors: RL
authors: Frost
authors: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
authors: Andrés
authors: A
authors: López
authors: School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
authors: Yunfei
authors: Y
authors: Xi
authors: Geology Department, School of Mines, Federal University of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto, MG 35 400-00, Brazil.
authors: Ricardo
authors: R
authors: Scholz
mesh_terms: D002118:Calcium / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D008903:Minerals; D010710:Phosphates; D014867:Water; D002118:Calcium
keywords: Hydroxyl; Infrared; Kapundaite; Phosphate; Raman spectroscopy; Wardite