THE CRYSTAL STRUCTURE OF BERTOSSAITE, CaLi2[Al4(PO4)4(OH,F)4]

Abstract

A sample of bertossaite {CaLi 2 [Al 4 (PO 4 ) 4 (OH,F) 4 ]} from the Buranga pegmatite, Rwanda, was investigated by single-crystal X-ray diffraction, electron microprobe, and infrared spectroscopic techniques. Under the polarizing microscope, bertossaite forms large xenomorphic grains reaching 500 mm in length, included in montebrasite and associated with quartz and a phosphate of the lazulite-scorzalite series. Electron-microprobe analyses indicate the empirical formula (Ca 0.83 Na 0.15 Sr 0.02 ) S1.00 (Li 1.86 Mn 0.10 Na 0.04 ) S2.00 [(Al 3.90 Fe 0.09 Mg 0.01 ) S4.00 (PO 4 ) 4 (OH 3.35 F 0.65 ) S4.00 ]; the mechanism of coupled substitution Li + + Ca 2+ = Mn 2+ + Na + explains the presence of Na at the Ca site and of Mn at the Li site. The crystal structure of bertossaite [Imcb, a 11.476(1), b 15.744(1), c 7.228(1) Å] is isotypic with that of palermoite {SrLi 2 [Al 4 (PO 4 ) 4 (OH) 4 ]}, and is based on dimers of edge-sharing AlO 6 octahedra, which are connected together via corner-sharing to form chains of octahedra running along the a axis. These chains are connected to adjacent chains by corner-sharing PO 4 tetrahedra, constituting a heteropolyhedral framework that contains large channels in which the Ca and Li atoms occur. A comparison between the OH…O distances calculated from the infrared spectrum, and those obtained from the structural data, allows one to assign the bands corresponding to the stretching vibrations of the (OH) groups.

Pilawite-(Y), Ca2(Y,Yb)2[Al4(SiO4)4O2(OH)2], a new mineral from the Piława Górna granitic pegmatite, southwestern Poland: mineralogical data, crystal structure and association

“…The [ [6] M 2 ( [4] TO 4 ) 4 j 2 ] chain occurs in the phosphate minerals palermoite, Sr 2 Li 4 [Al 2 (PO 4 ) 2 (OH) 2 ] 2 (Moore and Araki, 1975) (Hatert et al, 2011), and the arsenate mineral carminite, Pb[Fe 3+ 2 (PO 4 ) 2 (OH) 2 ] (Finney, 1963). The chains from pilawite-(Y) and palermoite are compared in Fig.…”

Spectral Investigations on Cu2+-doped Li2CaAl4(PO4)4F4 Phosphors

“…The diffracted data confirm the crystal system is orthorhombic and the lattice cell parameters evaluated as a = 1.145, b = 1.589, c = 0.726 nm, respectively. These lattice cell parameters are in tune with the reported Bertossaite earlier [23]. The average crystallite size of prepared sample is calculated using Scherrer's formula…”

“…-doped Li 2 CaAl 4 (PO 4 ) 4 F 4 phosphors are synthesized using a solidstate reaction method. The title compound prepared sample is similar to natural mineral Bertossaite [23]. The prepared sample was characterized by different spectroscopic techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), optical absorption and electron paramagnetic resonance (EPR) studies which give information about the crystal structure, morphology, site symmetry, optical properties and bonding nature, respectively.…”

Paragenesis and precipitation stages of Nb-Ta-oxide minerals in phosphorus-rich rare-element pegmatites (Buranga dike, Rwanda)

“…Bertossaite is mostly present as an alteration of montebrasite and trolleite but also occurs as inclusions in the latter. This indicates that the formation of bertossaite is not straightforward and should be interpreted with care since it could be stable in multiple stages and under variable conditions, possibly due to its structure being able to host multiple components (e.g., Li, Na, Ca, Sr, Al, Fe, Mn; Hatert et al, 2011b). In any case, bertossaite and CGM crystallization occur between the onset of the chemical remobilization by a fluid phase under magmatic conditions and the complete solidification of the dike.…”