Refinement of the crystal structure of ushkovite from Nevados de Palermo, República Argentina

The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, α 108.278(7), β 111.739(7), γ 71.626(7)°, V 351.55(6) Å3, Z = 2, space group P1, has been refined to an R index of 2.3% for 1781 observed reflections measured with MoKα X-radiation. The crystal used to collect the X-ray-diffraction data was subsequently analyzed with an electron microprobe, to give the formula (Mg0.97 Mn2+ 0.01) (H2O)4 [(Fe3+ 1.99 Al0.03) (PO4) (OH) (H2O)2]2 (H2O)2, with the (OH) and (H2O) groups assigned from bond-valence analysis of the refined structure. Ushkovite is isostructural with laueite. Chains of corner-sharing {Fe3+ O2 (OH)2 (H2O)2} octahedra extend along the c axis and are decorated by (PO4) tetrahedra to form [Fe3+ 2 O4 (PO4)2 (OH)2 (H2O)2] chains. These chains link via sharing between octahedron and tetrahedron corners to form slabs of composition [Fe3+ 2 (PO4)2 (OH)2 (H2O)2] that are linked by {Mg O2 (H2O)4} octahedra.Nous avons affiné la structure cristaline de l’ushkovite, triclinique, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, 108.278(7), 111.739(7), 71.626(7)°, V 351.55(6) Å3, Z = 2, groupe spatial P¯ 1, jusqu’à un résidu R de 2.3% en utilisant 1781 réflexions observées mesurées avec rayonnement MoK. Le même cristal a par la suite été analysé avec une microsonde électronique pour établir la formule chimique, (Mg0.97 Mn2+0.01) (H2O)4 [(Fe3+1.99 Al0.03) (PO4) (OH) (H2O)2]2 (H2O)2, les groupes (OH) et (H2O) étant assignés selon une annalyse des valences de liaison à partir de la structure affinée. L’ushkovite possède la même structure que la lauéite. Des chaînes d’octaèdres {Fe3+ O2 (OH)2 (H2O)2} liés par partage de coins sont parallèles à l’axe c et sont décorées avec des tétraèdres (PO4) pour former des chaînes de stoechiométrie [Fe3+2 O4 (PO4)2 (OH)2 (H2O)2]. Ces chaînes sont liées entre elles par partage de coins d’octaèdres et de tétraèdres pour former des panneaux de composition [Fe3+2 (PO4)2 (OH)2 (H2O)2]; à leur tour, ceux-ci sont liés par des octaèdres {Mg O2 (H2O)4}.Fil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Hawthorne, Frank C.. University of Manitoba; Canad

Prismatine: Revalidation for Boron-Rich Compositions in the Kornerupine Group

Kornerupine and prismatine were introduced independently by Lorenzen in 1884 (but published in 1886 and 1893) and by Sauer in 1886, respectively. Ussing (1889) showed that the two minerals were sufficiently close crystallographically and chemically to be regarded as one species. However, recent analyses of boron using the ion microprobe and crystal structure refinement, indicate that the boron content of one tetrahedral site in kornerupine ranges from 0 to 1. Kornerupine and prismatine, from their respective type localities of Fiskenaesset, Greenland and Waldheim, Germany, are distinct minerals, members of an isomorphic series differing in boron content. For this reason, we re-introduce Sauer\u27s name prismatine for kornerupines with B \u3e 0.5 atoms per formula unit (p.f.u.) of 22(O,OH,F), and restrict the name kornerupine sensu stricto to kornerupines with B \u3c 0.5 p.f.u. Kornerupine sensu lato is an appropriate group name for kornerupine of unknown boron content. Kornerupine sensu stricto and prismatine from the type localities differ also in Fe2+/Mg ratio, Si - (Mg + Fe2+ + Mn) content, Al content, F content, colour, density, cell parameters, and paragenesis. Both minerals formed under granulite-facies conditions with sapphirine and phlogopite, but kornerupine sensu stricto is associated with anorthite and homblende or gedrite, whereas prismatine is found with oligoclase (An9-13), sillimanite, garnet, and/or tourmaline. Occurrences at other localities suggest that increasing boron content extends the stability range of prismatine relative to that of kornerupine sensu stricto

EDGE-SHARING Mn2*Oo TETRAHEDRA lN THE STRUCTURE oF AKATORETTE, M n3*Al2Si8O24(OH)8

ABSTRACT The crystal strudure of akatoreite, Mn!*Alrsiroza(oH)s, a s.337Q), b 10.367(2)" c 7 .629(l) A, a 1M.46(1),0 93.81(2), y 104.18(l);, V 613.2(2) L3, fr, zol, has 6een solved'by direct methds and refined to an R index of 2.9Vo for 2691observed reflections measured with MoKo radiation. There are five independent Mn positions. Four ofthese are octahedrally coordinated by O2-and OH-anions, and the mean bond-Jengths at rhese sites show the Mn to be entirely in the divalent state. The fifth Mn position is tetrahedrally coordinated by four 02-anions, and the mean bondJength shows the Mn to be in the divalent state. Adjacent 6AnO; teuahedra share an edge to form an [Mn2O6] dimer. There is one Al position, coordinated by six anions in an octahedral arrangiment, and both site-scattering refinement and mean bond-length show no substitution of Fe'* or Mn'* for Al at fiis site. There are four distinct Si positions, all ofwhich are tetrahedrally coordinated; one ofthe silicate teuzhedra is an acid silicate group: SiO3(OH). The four Si tetrahedra form a linear [Si4O12(OH)] cluster, and akatoreite is thus a sorosilicate. The (MnQ) and (A106) octahedra (Q: unspecified ailon) form edge-sharing strips of octahedra three ocahedra wide, that extend along the a direction. These strips are cross-linked into sheets by the fMn2O6l tetrahe&al dimers, which share edges with the peripieral ctahedra of adjacent strips. The resultant sheets arc linked into a complex heteropolyhedral framework by the sorosilicate fragments and by a hydrogen-bond network. Relationships to other sorosilicates are reviewed. Keywords: akatoreite, crystal structure, silicate, sorosilicate, tetrahedrally coordinated divalent manganese. SoMMAIRE Nous avons affind la structure cristalline de l'akatoreite, Mne2+A12SisO24(OH)e, a 5.337(2), b 10.367(2), c 7.6290) A, u 104.46(l), F 93.31(2), y 104:18(l)",V613.2(\ L3, fl,Z= l, par m6thodes directes jusqu'b un r€siduRde2.9vo en utilisant 2691 r6flexions observ6es, mesurdes avec rayonnement Mo/(cr. ta structure contient cinq sites ind6pendants de Mn. Quatre d'entre eux sont en coordinenc€ octaddrique avec des anions 02* et OH-; dans chaque cas, la longueur moyenne des liaisons montre que le Mn est entibrement bivalent. Le Mn de la cinquidme position possbde une coordinence tdtra6drique avec quatre anions O'-; la longueur moyenne des liaisons montre que le Mn est bivalenl Les tdtrabdres (MnOa) adjacents partagent une a€te, pour former un dimbre [Mn2O6]. fl y a une position occupde par l'Al, entour6e de six anions formant un octaCdre. Un affinement des pouvoirs de dispersion dtette position, aussi bien que la longueur moyenne des liaisons, montrent qu'il n'y a aucun remplacement de I'Al par Fel* ou Mnh. [a structure comporte quatre positions distinctes occup€es pax Si, toutes i coordinence t6tra6drique. Dans un ias, il s'agit d'un groupe silicat6 acide: SiO;(OH). Les quatre t6trabdret 51 lottnsnl un alignement [Si4Ol2(OH)]; I'akatordite serait donc un sorosilicate. Les octabdres (MnOd et (At$) forment des rubans d'octabdres h a€tes parag€es, d'une largeur de trois octaidres, orient6s le long de a. Ces rubans sont li6s transversalement en feuillets par les dimbres de tdtrabdres MnzOel, qui partagent une a€te avec I'ocaddre Sriph6rique des rubans adjacents. I€s feuillets qui en r6sultent sont 1i6s en une uame complexe h6t6ropoly6drique par les fragments sorosilicat6s et un r6seau de liaisons hydrogbne. Nous examinons la relation de cette structure avec celle d'autres sorosilicates. (Iraduit par la R6daction) Mots-clls: akator6ite, structure cristalline, sitcate, sorosilicate, mangandse bivdLlent h coordinence t6tra6drique

An integrated study of uranyl mineral dissolution processes: etch pit formation, effects of cations in solution, and secondary precipitation

Understanding the mechanism(s) of uranium-mineral dissolution is crucial for predictive modeling of U mobility in the subsurface. In order to understand how pH and type of cation in solution may affect dissolution, experiments were performed on mainly single crystals of curite, Pb2+3(H2O)2[(UO2)4O4(OH)3]2, becquerelite, Ca(H2O)8[(UO2)6O4(OH)6], billietite, Ba(H2O)7[(UO2)6O4(OH)6], fourmarierite Pb2+1−x(H2O)4[(UO2)4O3−2x(OH)4+2x] (x= 0.00-0.50), uranophane, Ca(H2O)5[(UO2)(SiO3OH)]2, zippeite, K3(H2O)3[(UO2)4(SO4)2O3(OH)], and Na-substituted metaschoepite, Na1−x[(UO2)4O2−x(OH)5+x] (H2O)n. Solutions included: deionized water; aqueous HCl solutions at pH 3.5 and 2; 0.5mol L−1 Pb(II)-, Ba-, Sr-, Ca-, Mg-, HCl solutions at pH 2; 1.0mol L−1 Na- and K-HCl solutions at pH 2; and a 0.1mol L−1 Na2CO3 solution at pH 10.5. Uranyl mineral basal surface microtopography, micromorphology, and composition were examined prior to, and after dissolution experiments on micrometer scale specimens using atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Evolution of etch pit depth at different pH values and experimental durations can be explained using a stepwave dissolution model. Effects of the cation in solution on etch pit symmetry and morphology can be explained using an adsorption model involving specific surface sites. Surface precipitation of the following phases was observed: (a) a highly-hydrated uranyl-hydroxy-hydrate in ultrapure water (on all minerals), (b) a Na-uranyl-hydroxy-hydrate in Na2CO3 solution of pH 10.5 (on uranyl-hydroxy-hydrate minerals), (c) a Na-uranyl-carbonate on zippeite, (d) Ba- and Pb-uranyl-hydroxy-hydrates in Ba-HCl and Pb-HCl solutions of pH 2 (on uranophane), (e) a (SiOx(OH)4−2x) phase in solutions of pH 2 (uranophane), and (f) sulfate-bearing phases in solutions of pH 2 and 3.5 (on zippeite

Bobfergusonite from the Nancy pegmatite, San Luis range, Argentina: Crystal-structure refinement and chemical composition

A second occurrence of bobfergusonite, ideally Na2 Mn2+ 5 Fe3+ Al (PO4 6, has been discovered at the Nancy pegmatite, San Luis Range, Argentina. The Nancy pegmatite is a small, poorly evolved pegmatite of the beryl-columbite-phosphate subtype of rare-element pegmatites. Bobfergusonite from the Nancy pegmatite is monoclinic, a 12.796(3), b 12.465(2), c 11.001(2) Å, 97.39(3)°, V 1740.1(5) Å3, P21/n, Z = 4, has been refined to an R-index of 2.6% for 2959 observed (Fo ≥ 4σF) reflections measured with MoK α X-radiation on a Bruker P4 diffractometer equipped with a CCD detector. The crystal used for the collection of the X-ray intensity data was subsequently analyzed with an electron microprobe. The unit formula derived from the refined site-scattering values and electron-microprobe results is (Na1.10 □0.90) (Na0.90 □0.10) Mn2+ (Mn2+ 0.89 Ca0.11) (Fe2+ 0.91 Fe3+ 0.49 Mn2+ 0.32 Mg0.28) (Fe3+ 0.42 Fe2+ 0.28 Mg0.30) (Al0.94 Fe3+ 0.06) (PO4)6. In bobfergusonite, there are six M sites, each coordinated by six O-atoms in an octahedral arrangement with distances ranging from 1.918 Å at M(6) to 2.237 Å at M(2). There is strong order between the divalent and trivalent cations over the six M sites, and there is also strong order between Al and Fe3+. There are five X sites, X(1)-X(5), each having a wide dispersion of X-O distances. The X(1) site is mainly occupied by Mn2+ and has octahedral coordination. The X(2) and X(3) sites are each [8]-coordinated, the X(4) and X(5) sites are [7]-coordinated, and X(2)-X(5) are all approximately half-occupied by Na. In all of the alluaudite-related structures, the M sites form linear edge-sharing trimers, and the alluaudite, wyllieite and bobfergusonite structures show subtly different patterns of cation order-disorder. Bobfergusonite crystals from both known localities, the Nancy pegmatite (Argentina) and the Cross Lake pegmatite (Manitoba), are considerably disordered.Un deuxième exemple de bobfergusonite, de formule idéale Na2 Mn2+5 Fe3+ Al (PO4)6, a été découvert, celui-ci dans la pegmatite de Nancy, chaîne de San Luis, en Argentine. Cette pegmatite est de taille restreinte, et constitue un exemple peu évolué du sous-type à béryl – columbite – phosphate des pegmatites à éléments rares. La bobfergusonite de cet indice est monoclinique, a 12.796(3), b 12.465(2), c 11.001(2) Å, 97.39(3) , V 1740.1(5) Å3 , P21/n, Z = 4; nous en avons affiné la structure jusqu’à un résidu R de 2.6% pour 2959 réflexions observées (|Fo| ‡ 4F), mesurées avec un diffractomètre Bruker P4 muni d’un détecteur CCD (rayonnement MoK ). Le cristal utilisé a ensuite été analysé avec une microsonde électronique. L’unité formulaire dérivée à partir des valeurs affinées de la dispersion des sites et des résultats des données obtenues à la microsonde électronique est (Na1.10 0.90) (Na0.90 0.10) Mn2+ (Mn2+0.89 Ca0.11) (Fe2+0.91 Fe3+0.49 Mn2+0.32 Mg0.28) (Fe3+0.42 Fe2+0.28 Mg0.30) (Al0.94 Fe3+0.06) (PO4)6. La structure contient six sites M, chacun coordonné par six atomes d’oxygène dans un agencement octaédrique, avec les distances entre 1.918 Å pour M(6) jusqu’à 2.237 Å pour M(2). Il y a une forte mise en ordre entre les cations bivalents et trivalents sur les six sites M, et il y a aussi une forte mise en ordre entre Al et Fe3+. La structure contient cinq sites X, X(1)–X(5), chacun faisant preuve d’une grande dispersion des distances X–O. Le site X(1) est surtout rempli par le Mn2+ et possède une coordinence octaédrique. Les sites X(2) et X(3) ont chacun une coordinence [8], et les sites X(4) et X(5), une coordinence [7]; les sites X(2)– X(5) sont tous environ à moitié remplis par le Na. Dans tous les membres du groupe de l’alluaudite, les sites M forment des groupes trimériques linéaires d’octaèdres à arêtes partagées, et les structures de l’alluaudite, la wyllieïte et la bobfergusonite possèdent des degrés d’ordre et désordre subtilement différents. Les cristaux de bobfergusonite des deux localités, la pegmatite de Nancy, en Argentine, celle de Cross Lake, au Manitoba, sont considérablement désordonnés.Fil: Tait, Kimberly T.. University of Manitoba; CanadáFil: Hawthorne, Frank C.. University of Manitoba; CanadáFil: Cerny, Petr. University of Manitoba; CanadáFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Bismutotantalite from northwestern Argentina: Description and crystal structure

Bismutotantalite occurs in albite-rich cores of the La Elvirita granitic pegmatites, northwestern Argentina, associated mainly with bismuth, bismuthinite, ferrotapiolite, manganotantalite, microlite, uranmicrolite, bismutomicrolite, hafnian zircon and montebrasite. A fresh, cm-sized crystal, dark grey with a greasy luster and D = 8.809 g/cm3, was examined. In reflected light, it is grey with very weak bireflectance; two phases can be distinguished. Electron-microprobe analysis gives the host bismutotantalite [Bi] as [Bi,Sb], (Bi0.68Sb0.32)(Ta0.89Nb0.11)O4, is enriched in Sb. Least-squares refinement of X-ray powder-diffraction data of [Bi] gave a 4.968(1), b 11.796(3), c 5.646(1) Å, V = 330.85(9) Å3. The crystal structures of [Bi] and [Bi,Sb] were refined to R indices of 1.9 and 2.4%, based on 387 and 377 observed (4σ) reflections, respectively, measured with MoKα X-radiation. Both phases are orthorhombic, space group Pcnn. Z = 4; [Bi] has a 4.9652(4), b 11.7831(16), c 5.6462(5) Å. V 330.32(6) Å3, and [Bi,Sb] has a 4.9471(4), b 11.7878(7), c 5.6048(3) Å, V 326.83(4) Å3. These results show that the centrosymmetric structure of bismutotantalite can accommodate up to ∼40% Sb3+ substituting for Bi3+ without changing to the Pc21n structure of stibiotantalite.Fil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Direccion Nacional del Antártico. Instituto Antártico Argentino. Instituto Antártico Argentino - Sede Cricyt (Mendoza); ArgentinaFil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Ministerio de Relaciones Exteriores, Comercio Internacional y Culto. Direccion Nacional del Antártico. Instituto Antártico Argentino. Instituto Antártico Argentino - Sede Cricyt (Mendoza); ArgentinaFil: Cooper, Mark A.. University of Manitoba; CanadáFil: Cerný, Petr. University of Manitoba; CanadáFil: Hawthorne, Frank C.. University of Manitoba; Canad