Jörgen Langhof

Chiavennite and zoned genthelvite-helvite as late-stage minerals of the Proterozoic LCT pegmatites at Utö, Stockholm, Sweden

Abstract The Utö pegmatite system is host to a plethora of late-formed minerals, most of which have not been detected in previous studies of this classical locality. Among them are minerals that developed in cracks and druses, including a number of beryllosilicates, like the zeolite chiavennite, genthelvite-helvite, milarite and bavenite; Mn-rich minerals such as manganite, wickmanite and friedelite; and several sulphides. The parageneses and crystal chemistry of chiavennite and genthelvite-helvite are the focus of the present paper. Chiavennite was analysed using electron and ion-microprobe techniques, and was found to contain significant amounts of B substituting for Be: a structural formula for one sample is (Ca0.93Na0.07)Mn0.77Fe2+ 0.10Ca0.07Fe3+ 0.06Mg0.01) [Be1.86B0.15][Si4.68Al0.32]O12.86(OH)2.14 · 2H2O. The corresponding orthorhombic unit-cell parameters are a = 8.907(4), b = 31.227(9), and c = 4.777(2) Å. The genthelvite-helvite grains, often arranged in polycrystalline aggregates, are zoned discontinuously reflecting variations in Mn and Zn contents. Generally, they have Mn-rich cores and Zn-dominant rims (consisting of up to 93 mol.% of the genthelvite end-member). The late-stage Be minerals are products of low-temperature alteration of primary beryl under the influence of Ca- and Mn-rich fluids.

Late‐stage beryllium silicates from the Sels‐Vitberget granitic pegmatite, Kramfors, central Sweden

Abstract The beryllium silicates bertrandite, euclase, and phenakite have been identified replacing primary beryl in a small alteration zone in the upper part of the Sels‐Vitberget pegmatite. Within a few square metres of outcrop, beryl crystals intergrown with microcline perthite are more or less completely altered to a coarsely crystalline and drusy mixture of Be silicates and quartz. Some seriate and minor apatite also occur in this association. The beryl pseudomorphs exhibit a diffuse zoning, with the core portion dominated by the most common Be silicate, bertrandite. Euclase occurs in lesser amounts, often intergrown with bertrandite. Phenakite is more rare and generally confined to finer‐grained drusy border rims of the former beryl crystals; the texture indicates that phenakite is not in equilibrium with bertrandite + euclase (+ quartz). The formation of Be silicates at Sels‐Vitberget is apparently related to the percolation of gradually evolving, late‐stage, acid to neutral fluids on a local scale...

Single-crystal Raman spectroscopy of natural paulmooreite Pb2As2O5 in comparison with the synthesized analog

Abstract The single-crystal Raman spectra of the natural mineral paulmooreite Pb2As2O5 from the Långban, Filipstad district, Värmland province, Sweden, are presented for the first time. It is a monoclinic mineral containing an isolated [As2O5]4- dimer. Unpolarized single-crystal spectra of the natural and synthetic samples compare favorably with each other and are characterized by strong bands around 186 and 140 cm-1 and three medium bands at 800-700 cm-1. Band assignments were made based on band symmetry and spectral comparison between experimental band positions and those resulting from Hartree-Fock calculation of an isolated [As2O5]4- anion complex. Spectral comparison was also made with lead arsenites such as synthetic PbAs2O4 and Pb2(AsO2)3Cl and natural finnemanite to determine the contribution of the terminal and bridging O in paulmooreite. Bands at 760-733 cm-1 were assigned to terminal As-O vibrations, whereas stretches of the bridging O occur at 562 and 503 cm-1. The single-crystal spectra showed good mode separation, allowing bands to be assigned a symmetry species of Ag or Bg.

Wiklundite, ideally Pb2[4](Mn2+,Zn)3(Fe3+,Mn2+)2(Mn2+,Mg)19(As3+O3)2[(Si,As5+)O4]6(OH)18Cl6, a new mineral from Långban, Filipstad, Värmland, Sweden: Description and crystal structure

Abstract Wiklundite, ideally Pb2[4](Mn2+,Zn)3(Fe3+,Mn2+)2(Mn2+,Mg)19 (As3+O3)2[(Si,As5+)O4]6(OH)18Cl6, is a new arseno-silicate mineral from Långban, Filipstad, Värmland, Sweden. Both the mineral and the name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2015-057). Wiklundite and a disordered wiklundite-like mineral form radiating, sheaf-like aggregates (up to 1 mm long) of thin brownish-red and slightly bent lathshaped crystals. It occurs in a dolomite-rich skarn in association with tephroite, mimetite, turneaurite, johnbaumite, jacobsite, barite, native lead, filipstadite and parwelite. Wiklundite is reddish brown to dark brown, and the streak is pale yellowish brown. The lustre is resinous to sub-metallic, almost somewhat bronzy, and wiklundite does not fluoresce under ultraviolet light. The calculated density is 4.072 g cm-3. Wiklundite is brittle with an irregular fracture, and has perfect cleavage on {001}; no parting or twinning was observed. Wiklundite is uniaxial (-), orange red and non-pleochroic in transmitted light, but shows incomplete extinction and distorted interference figures, preventing complete determination of optical properties. Electron-microprobe analysis (H2O calculated from the structure) of wiklundite gave SiO2 11.17, Al2O3 0.06, Fe2O3 4.46, As2O5 0.75, As2O3 6.81, MnO 47.89, ZnO 0.78, CaO 0.09, PbO 14.48, Cl 6.65, H2O 5.18, O=Cl2 -1.50, total 97.11 wt.%, As valences and H2O content taken from the crystal-structure refinement, and Fe3+/(Fe2+ + Fe3+) determined by Mössbauer spectroscopy. Wiklundite is hexagonalrhombohedral, space group R3c, a = 8.257(2), c = 126.59(4) Å, V = 7474(6) Å3, Z = 6. The crystal structure of wiklunditewas solved by direct methods and refined to a final R1 index of 3.2%. The structure consists of a stacking of five layers of polyhedra: three layers consist of trimers of edge-sharing Mn2+-dominant octahedra linked by (SiO4) tetrahedra, (Fe3+(OH)6) dominant octahedra and (AsO3) triangular pyramids; one layer of corner-sharing (SiO4) and (Mn2+O4) tetrahedra; and one layer of (Mn2+Cl6) octahedra and (Pb2+(OH)3Cl6) polyhedra. The mineral is named after Markus Wiklund (b. 1969) and Stefan Wiklund (b. 1972), the well-known Swedish mineral collectors who jointly found the specimen containing the mineral.

Metamorphic harkerite from nordmarks odalfält, Värmland, sweden

Abstract Harkerite associated with calcite, vesuvianite, tephroite, jacobsite, spinel, clintonite, etc. has been identified in museum specimens from the ore field Nordmarks odalfalt. It is optically isotropic and the cubic (sub)cell parameter is 14.722(1) A. Partial chemical analysis yields MgO 9.5, A12O3 2.3, SiO2 11.0, CaO 46.6, MnO 1.5, Fe2O3 0.5, Cl 2.4 (all in wt.%). It is concluded that this harkerite formed through metamorphism of a boron‐rich protolith, rather than by metasomatic reactions involving magmatic fluids, which has been inferred for earlier finds of the mineral. Holtstam, D. & Langhof, J., 1995: Metamorphic harkerite from Nordmarks odalfalt, Varmland, Sweden. GFF, Vol. 117 (Pt. 3, September), pp. 151–152. Stockholm. ISSN 1103–5897.