Ferrorosemaryite, NaFe2+Fe3+Al(PO4)3, a new phosphate mineral from the Rubindi pegmatite, Rwanda

Abstract

Among the four valid type-minerals reported in Rwanda, three were described in the Buranga pegmatite, which is host to over hundred of other mineral species (Daltry & Von Knorring, 1998). More than half of the recorded minerals from Buranga are phosphates, of which two compositional groups are recognised: Al-dominant and Fe-Mn-dominant phases (Von Knorring, 1970). Whereas the phosphate mineralogy of the Buranga pegmatite is relatively well known, detailed descriptions of phosphate mineral associations occurring in other granitic pegmatites from the Gatumba field are not really abundant. In order to complete the mineralogical description of these associations and to discuss their petrography, Lefèvre (2003) thoroughly investigated several samples collected in the Rubindi-Kabilizi pegmatites by A.-M. F., F.F. and P.K. in 1983. These samples contained aluminum phosphates, mostly montebrasite and scorzalite, with bertossaite, brazilianite, and trolleite.Embedded in a few scorzalite-rich samples from Rubindi, a dark green mineral was observed. A preliminary examination under the polarizing microscope and by powder X-ray diffraction indicated that this mineral belongs to the alluaudite or wyllieite group of minerals. The electron microprobe analyses indicated the presence of aluminium in significant amounts, thus confirming the identification of a wyllieite-type phosphate. The P2 1 /n space group of wyllieite was furthermore confirmed by Weissenberg photographs.This mineral corresponds to the Fe 2+ -rich equivalent of rosemaryite, i.e. I I NaFe 2+ Fe 3+ Al(PO 4 ) 3 , not yet described.

The Association Qingheiite - Beusite - Lithiophilite in the Santa Ana Pegmatite, San Luis, Argentina

“…Fransolet (1995) interpreted the rosemaryite from the Buranga pegmatite, associated with secondary phosphates such as trolleite, as possibly originating by the oxidation of wyllieite. Likewise, Hatert et al (2005) described ferrorosemaryite, closely associated with trolleite, scorzalite and other low-temperature phosphatic phases. In addition, similar pegmatitic phosphates with Fe 3+ , such as bobfergusonite (Ercit et al 1986, Tait et al 2004) and even ferrisicklerite (Roda Robles et al 1998), are claimed to be primary and magmatic, whereas minerals considered typically primary are locally found to be metasomatic products (e.g., wolfeite; Masau et al 2000).…”

THE CRYSTAL STRUCTURE AND CRYSTAL CHEMISTRY OF MANITOBAITE, IDEALLY (Na16 )Mn2+ 25Al8(PO4)30, FROM CROSS LAKE, MANITOBA

“…7b), and Fe 2+ or Mn 2+ (or both) occupies the M(1) site. There are two end-member patterns of order: in rosemaryite and ferrorosemaryite (Hatert et al 2005(Hatert et al , 2006, M(2a) = Al and M(2b) = Fe 2+ (Fig. 7b, top), whereas in ferrowyllieite (Moore & Molin-Case 1974), M(2a) = Fe 2+ and M(2b) = Al (Fig.…”

The transition from alluaudite- to wyllieite-type phosphates: which is the role really played by aluminium?

“…Between 300 and 600°C, white powders without visible crystals were obtained, and the powder X-ray diffraction patterns correspond to those of alluaudite-type phosphates, without any supplementary reflection typical of the P2 1 /n wyllieite space group. As discussed by Hatert et al [2], however, the identification of actual wyllieite-type phosphates can only be confirmed by single-crystal X-ray diffraction techniques. At 700°C/3.5 kbar and 800°C/1 kbar, tiny acicular crystals were obtained and single-crystal structure refinements indicated an alluaudite-type structure [5].…”

“…Nature of these globules is supposed to be fullerene-like. Due to appeared to the present time to high-resolution scanning probe microscopic methods difficulties with visualization nanometrical structural elements of metastable natural substances are removed [1,2]. We applied scanning tunneling (STM) and atomic force (AFM) microscopes.…”

“…Consequently, the C2/c space group of alluaudite transforms into P2 1 /n in wyllieite, with no significant change of the unit-cell parameters, and with a structural formula which corresponds to X(2)X(1a)X(1b)M(1)M(2a) M(2b)(PO 4 ) 3 [1]. Recently, the description of the new mineral species ferrorosemaryite, NaFe 2+ Fe 3+ Al(PO 4 ) 3 , in the Rubindi pegmatite, Rwanda, initiated a detailed mineralogical study of the wyllieite group of minerals [2,3]. This study indicates that aluminium is localized on the M(2a) site of rosemaryite and ferrorosemaryite, not on the M(2b) site as observed in ferrowyllieite [1].…”