Vätmanlandite-(Ce) - A new lanthanide- and F-bearing sorosilicate mineral from Vätmanland, Sweden: Description, crystal structure, and relation to gatelite-(Ce)
- Autor(en)
- D Holtstam, Uwe Kolitsch, U B Andersson
- Abstrakt
Vašstmanlandite-(Ce), ideally (Ce,La)3CaAl2Mg2[Si2O 7][SiO4]3F(OH)2, is a new mineral species from the Vašstmanland county, Bergslagen region, Sweden. Together with more Fe-rich, F-poor members, it forms solid solutions that are important for lanthanide sequestration in the Bastnašs-type skarn deposits in Vašstmanland. At the type locality (Malmkašrra, Norberg district) it occurs as anhedral grains 0.2-3 mm across, in association with fluorbritholite-(Ce), tremolite, a serpentine mineral, magnetite, dollaseite-(Ce) and dolomite. The mineral is allanite-like in appearance; it is dark brown, translucent, with vitreous luster, and has good cleavage parallel to ?001?, uneven to conchoidal fracture, and a yellowish gray streak; D calc = 4.51(2) gžcm-3 and Mohs hardness = 6. Optically it is biaxial (-), with a = 1.781(4), ßcalc = 1.792, ? = 1.810(4) and 2Va = 75(5)°. Chemical analysis by electron-microprobe and 57Fe Mošssbauer spectroscopy yield: La 2O3 13.65, Ce2O3 23.90, Pr2O3 2.07, Nd2O3 6.28, Sm2O3 0.42, Gd2O3 0.15, Y2O3 0.18, CaO 4.65, FeO 1.14, Fe 2O3 2.69, MgO 5.51, Al2O 3 8.58, TiO2 0.04, P2O5 0.05, SiO2 26.61, F 1.06, H2Ocalc 1.61, O = F -0.45, sum 98.14. Vašstmanlandite-(Ce) is monoclinic, P21 /m, with a = 8.939(1), b = 5.706(1), c = 15.855(2) A°, ß = 94.58(1)°, V = 806.1(2) A°3, and Z = 2 (single-crystal data). The eight strongest lines in the X-ray powder diffraction pattern are [d (in A°) (I/ I0)(hkI)]: 15.81(16)(001), 4.65(10)(111), 3.50(20)(210), 2.983(100)(114), 2.685(13 (121), 2.678(11)(205¯), 2.625(19)(3 11¯), and 2.187(15 (402¯). The crystal structure was determined using single-crystal X-ray diffraction data and refined to R1(F) = 1.73 % for 2864 'observed' reflections with F0 > 4s(F0). Vaš stmanlandite-(Ce) is nearly isotypic to gatelite-(Ce), ideally Ce 3CaAl2AIMg[Si2O7][SiO4]3O(OH)2, and can be described as a regular dollaseite-(Ce)-tošrnebohmite-(Ce) polysome. The occurrence of extremely weak, continuous streaking in the diffraction patterns, and the presence of two pairs of mirror-related atoms in the tošrnebohmite-(Ce) module indicate that the structure model represents an average structure, unlike the situation in gatelite-(Ce) where there are no continuous streaks but instead, due to atomic ordering, sharp superstructure reflections resulting in a different unit cell. Œ 2005 E. Schweizerbart'sche Verlagsbuchhandlung.
- Organisation(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- Swedish Museum of Natural History, Uppsala University
- Journal
- European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences
- Band
- 17
- Seiten
- 129-141
- Anzahl der Seiten
- 13
- ISSN
- 0935-1221
- DOI
- https://doi.org/10.1127/0935-1221/2005/0017-0129
- Publikationsdatum
- 2005
- Peer-reviewed
- Ja
- ÖFOS 2012
- 1051 Geologie, Mineralogie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/a508d21a-0961-4de2-ab2c-528efa218951