Stavelotite-(La), a new lanthanum-manganese-sorosilicate mineral from the Stavelot Massif, Belgium

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doi: 10.1127/0935-1221/2005/0017-0703
Authors:Bernhardt, Heinz-Jürgen; Armbruster, Thomas; Fransolet, André-Mathieu; Schreyer, Werner
Author Affiliations:Primary:
Ruhr-Universität, Institut für Geologie, Bochum, Federal Republic of Germany
Other:
University of Bern, Switzerland
Université de Liège, Belgium
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 17(5), p.703-714. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:2005
Note:In English. 26 refs.; illus., incl. 6 tables
Summary:Stavelotite-(La) occurs as an accessory opaque mineral in a late quartz vein cross-cutting the deep purple manganiferous phyllites of Ordovician age at Le Coreux, near Salmchâteau, Belgium; it is associated with hematite, braunite, hollandite-strontiomelane, kanonaite, Mn-oxides, albite and muscovite. It appears as roundish to rectangular, generally equidimensional masses 10-160 <m in diameter; reflectance ∼ 14 %; in reflected light it is grey; Dcalc 4.489 g/cm3. EPMA gave SiO2 20.17, TiO2 0.44, MnO2 4.83, Mn2O3 31.67, MnO 5.99, Al2O3 3.30, Fe2O3 13.08, Sc2O3 1.47, La2O3 8.39, Nd2O3 3.39, Ce2O3 0.44, CaO 0.33, MgO 1.06, CuO 2.11, CoO 0.18, = 96.86, leading to the simplified formula La3Mn2+3Cu(Mn3+,Fe3+,Mn4+)26[Si2O7]6O30. Indexed XRD powder data are tabulated; strongest lines 2.7232(100), 2.7789(40),1.6635(40), 5.446(31), 1.6687(28) Å; a 11.525, c 33.347 Å, V 3836 Å3, Z = 3, space group P31. The crystal structure has been determined and refined to R 13.32%; it is very complex and densely packed, with four different polyhedral layers stacked parallel to the c axis: layer 1 consists of eight-coordinated distorted cube sites for Mn2+ sharing edges with strongly distorted Mn3+ polyhedra (tetragonal bipyramids), and also contains one planar square site for Cu2+. Layer 2 has more regular octahedra for Mn3+ as well as for the Mn4+ required for charge balance, and it contains SiO4 tetrahedra oriented in one direction. Layer 3 contains additional SiO4 tetrahedra oriented in two different opposing direction in order to link with those of layers 2 and 4, thus forming [Si2O7] groups, and it carries La in eightfold coordination. Layer 4 is of similar architecture to layer 2, but in an inverted position. Layers 1, 2 and 4 are geometrically similar to respective layers in the structure of langbanite. Stavelotite-(La) is the first REE silicate mineral to contain only large amounts of Mn (with some Fe) as additional cations. [R.A.H.]
Sections:Crystal structure; Mineral data; New minerals
Mineral Groups:Ortho-and ring silicates
Subjects:Chemical composition; Crystal chemistry; Crystal structure; Lanthanum; Manganese; Metals; New minerals; Orthosilicates; Rare earths; Silicates; Sorosilicates; Ardennes; Belgium; Europe; Stavelot-Venn Massif; Western Europe; Stavelotite
Abstract Numbers:05M/3713
Record ID:2005074502
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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