Västmanlandite-(Ce) - a new lanthanide- and F-bearing sorosilicate mineral from Västmanland, Sweden: description, crystal structure, and relation to gatelite-(Ce)
- Author(s)
- D Holtstam, Uwe Kolitsch, U B Andersson
- Abstract
Västmanlandite-(Ce), ideally (Ce,La)3CaAl2Mg2[Si2O7][SiO4]3F(OH)2, is a new mineral species from the Västmanlandcounty, Bergslagen region, Sweden. Together with more Fe-rich, F-poor members, it forms solid solutions that are important forlanthanide sequestration in the Bastnäs-type skarn deposits in Västmanland. At the type locality (Malmkärra, Norberg district) itoccurs 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 hasgood cleavage parallel to {001}, uneven to conchoidal fracture, and a yellowish gray streak; Dcalc = 4.51(2) g•cm-3 andMohs hardness» 6.Optically it is biaxial (-),with [ = 1.781(4), q calc = 1.792, * = 1.810(4) and 2V [ = 75(5)°. Chemical analysis by electron-microprobeand 57FeMössbauer spectroscopy yield: La2O3 13.65, Ce2O3 23.90, Pr2O3 2.07, Nd2O3 6.28, Sm2O3 0.42, Gd2O3 0.15, Y2O3 0.18, CaO4.65, FeO 1.14, Fe2O3 2.69, MgO 5.51, Al2O3 8.58, TiO2 0.04, P2O5 0.05, SiO2 26.61, F 1.06, H2Ocalc 1.61, O F –0.45, sum 98.14.Västmanlandite-(Ce) is monoclinic, P21/m, with a = 8.939(1), b = 5.706(1), c = 15.855(2) Å, q = 94.58(1)°, V = 806.1(2) Å3, and Z =2 (single-crystal data). The eight strongest lines in the X-ray powder diffraction pattern are [d (in Å) (I/I0)(hkl)]: 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)(311), and 2.187(15)(402). The crystalstructurewas determined using single-crystalX-ray diffraction data and refined to R1(F) = 1.73%for 2864 ’observed’ reflectionswithFo > 4 c (Fo). Västmanlandite-(Ce) is nearly isotypic to gatelite-(Ce), ideally Ce3CaAl2AlMg[Si2O7][SiO4]3O(OH)2, and can bedescribed as a regular dollaseite-(Ce)–törnebohmite-(Ce) polysome. The occurrence of extremely weak, continuous streaking in thediffraction patterns, and the presence of two pairs of mirror-related atoms in the törnebohmite-(Ce) module indicate that the structuremodel represents an average structure, unlike the situation in gatelite-(Ce) where there are no continuous streaks but instead, due toatomic ordering, sharp superstructure reflections resulting in a different unit cell.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Swedish Museum of Natural History, Uppsala University
- Journal
- European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences
- Volume
- 17
- Pages
- 129-141
- No. of pages
- 13
- ISSN
- 0935-1221
- Publication date
- 2005
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography, 104006 Solid state chemistry, 1051 Geology, Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/b8675c57-13e8-44df-a3d2-4919d7e6b9ab