Vibrational spectroscopic characterization of the phosphate mineral kulanite Ba(Fe(2+),Mn(2+),Mg)2(Al,Fe(3+))2(PO4)3(OH)3.
The mineral kulanite BaFe2Al2(PO4)3(OH)3, a barium iron aluminum phosphate, has been studied by using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscopy with EDX shows the mineral is homogenous with no other phases present. The Raman spectrum is dominated by an intense band at 1022cm(-1) assigned to the PO4(3-)ν1 symmetric stretching mode. Low intensity Raman bands at 1076, 1110, 1146, 1182cm(-1) are attributed to the PO4(3-)ν3 antisymmetric stretching vibrations. The infrared spectrum shows a complex spectral profile with overlapping bands. Multiple phosphate bending vibrations supports the concept of a reduction in symmetry of the phosphate anion. Raman spectrum at 3211, 3513 and 3533cm(-1) are assigned to the stretching vibrations of the OH units. Vibrational spectroscopy enables aspects on the molecular structure of kulanite to be assessed.
On the Crystal-Chemistry of Bjarebyite, BaMn2+2Al2(PO4)3(OH)3, From the Palermo #1 Pegmatite, Grafton County, New Hampshire, Usa
Abstract Bjarebyite, BaMn 2+ 2 Al 2 (PO 4 ) 3 (OH) 3 , is a rare secondary phosphate mineral in granitic pegmatites. From the crystallographic point of view it is exhaustively described in the monoclinic unit cell with a 9.0671(2) A, b 12.1500(4) A, c 4.9403(1) A, β 100.399(2)°, V 535.31(2) A 3 , and space group P 2 1 / m . Single crystal X-ray diffraction data were collected with Mo K α radiation. The hydrogen positions were located by difference Fourier map and refined in the final steps of the crystal structure anisotropic refinement, leading to an R index of 1.99%. A very good agreement was found with microprobe chemical analyses and bond valence calculations which show expected values for all the atomic sites. These features were confirmed by comparing the Raman spectra of bjarebyite and kulanite.
Structure and twinning in spencerite
Summary A refinement of the crystal structure of spencerite, Zn4(PO4)2(OH)2·3H2O, was performed on a twin crystal from Salmo, British Columbia. Three-dimensional intensity data were collected by a Weissenberg apparatus. The R index was 0·098 for 335 independent observed reflections. The crystal structure previously determined is essentially confirmed. Co-ordination around Zn is both octahedral and tetrahedral. The atomic arrangement consists of complex sheets of co-ordination octahedra and tetrahedra around Zn and P atoms connected by layers of water molecules. The frequent occurrence of twinning in spencerite is explained from structural considerations.