Vandermeerscheite, a New Uranyl Vanadate Related to Carnotite, from Eifel, Germany
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Journal of Geosciences, 64 (2019), 219–227 DOI: 10.3190/jgeosci.288 Original paper Vandermeerscheite, a new uranyl vanadate related to carnotite, from Eifel, Germany Jakub PlášIl1*, Anthony R. KAmPf2, Radek Škoda3, Jiří ČeJKA4 1 Institute of Physics, Academy of Sciences of the Czech Republic v.v.i, Na Slovance 1999/2, 182 21 Prague 8, Czech Republic; [email protected] 2 Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA 3 Department of Geological Sciences, Faculty of Science, Masaryk University, Kotlářská 2, 611 37, Brno, Czech Republic 4 Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Prague 9, Czech Republic * Corresponding author Vandermeerscheite (IMA2017-104), K2[(UO2)2V2O8]·2H2O, is a new uranyl-vanadate mineral from the Schellkopf quarry, Eifel, Germany. The new mineral occurs in cavities of volcanic rocks, mostly growing on phillipsite-K. It forms rosette- like aggregates of thin blades up to 50 µm long. Crystals are flattened on {10¯1 }, and elongated on [101], with crystal forms {010}, {10¯1 } and {111}; crystals are transparent with a vitreous luster. Vandermeerscheite is non-fluorescent under both long- and short-wavelength ultraviolet radiation. The Mohs hardness is ~2. The calculated density is 4.502 g·cm–3 based on the empirical formula; 4.507 g·cm–3 for the ideal formula. Vandermeerscheite dissolves easily in dilute HCl at room temperature. The new mineral is biaxial (–), with α = 1.83 (calc.), β = 1.90(1), γ = 1.91(1) (measured in white light at 22 °C). The measured 2V is 40(10)° estimated from conoscopic observation of interference figure; disper- sion is moderate r < v. No pleochroism was observed. Optical orientation is X ≈ {10¯1 }, Y ≈ [101], Z = b. The empiri- cal formula of vandermeerscheite (on the basis of 14 O apfu) is (K1.87Ca0.05Na0.04)Σ1.96[(U1.005O2)2V1.99O8]·2H2O. Raman 2+ ⊥ spectrum is dominated by the vibrations of UO2 and V2O8 units. Vandermeerscheite is monoclinic, P21/n, a = 8.292(2), b = 8.251(3), c = 10.188(3) Å, β = 110.84(3)°, V = 651.4(4) Å3, and Z = 2. The seven strongest powder X-ray diffraction lines are [dobs, Å (I, %) (hkl) ]: 7.49 (100) (¯1 01), 4.147 (22) (020), 3.738 (32) (¯2 02), 3.616 (20) (¯1 21), 3.254 (31) (112, 121), 3.132 (21) (¯1 22, 022), 2.989 (41) (211, 013). The crystal structure of vandermeerscheite was refined from the single-crystal X-ray data to R = 0.0801 for 644 independent observed reflections, withI obs > 3σ(I). The structure, which differs from carnotite in symmetry, is based upon uranyl vanadate sheets of francevillite topology; in the interlayer, there + are K cations and H2O groups that provide inter-sheet linkage. The new mineral honors Belgian amateur mineralogist and famous mineral photographer Eddy Van Der Meersche, who discovered the new mineral. Keywords: vandermeerscheite, uranyl vanadate, new mineral, carnotite group, crystal structure Received: 16 May 2019; accepted: 26 September 2019; handling editor: J. Sejkora The online version of this article (doi: 10.3190/jgeosci.288) contains supplementary electronic material. 1. Introduction by Hentschel and investigated in 1993 by Piret and co-workers – is a new species and provided us with Uranyl-vanadate minerals are relatively insoluble over a specimens for a new, detailed study. This new mineral range of pH conditions (circumneutral and alkaline) and description is based on three cotype specimens depos- they are quite abundant in Colorado Plateau-type U–V ited in the collections of the Natural History Museum deposits, as well as in the mine and mill tailings (Evans of Los Angeles County, 900 Exposition Boulevard, Los and Garrels 1958; Dahlkamp 1993; Spano et al. 2017; Angeles, CA 90007, USA, catalogue numbers 67260, Kampf et al. 2019). The most well-known and abundant 67261 and 67262. The new mineral and the name have of these is carnotite, K2(UO2)2(V2O8)·nH2O (where n been approved by the International Mineralogical As- is usually given in the range 1–3). Here we describe a sociation (IMA2017–104). new mineral from Schellkopf, Eifel (Germany), vander- meerscheite, K2[(UO2)2V2O8]·2H2O, which is chemically closely related to carnotite. 2. Occurrence Vandermeerscheite is named in honor of prominent Belgian amateur mineralogist, mineral collector and The new mineral was found in the quarry at Schellkopf distinguished mineral photographer Eddy Van Der near Brenk, Eifel, Rhineland-Palatinate, Germany. The Meersche (born 1945) living in Ghent, Belgium. He has quarry is located in a c. 380,000 year-old phonolitic long been convinced that this rarely found carnotite- dome, composed of dense porphyric selbergite that de- related mineral from Schellkopf – first noted in 1983 forms strata of Devonian shales (Cruse 1986; Meyer www.jgeosci.org Jakub Plášil, Anthony R. Kampf, Radek Škoda, Jiří Čejka 1988). In the massive and fine-grained rock, rich in po- phillipsite-K (Fig. 1) and, rarely, on fluorite. Sometimes tassium, phenocrysts of nosean are abundant. Sanidine, it forms also as inclusions in calcite. leucite and titanite are less common. The supergene mineralization is partly pneumatolytic, but mostly hydro- thermal, and is located in small vugs. The vug walls are 3. Physical and optical properties mostly covered with zeolites (most commonly “phillip- site”, frequently gonnardite intergrown with paranatrolite Vandermeerscheite occurs in crystals, which are thin and occasionally analcime, gismondine-Ca, chabazite-Ca blades up to 50 µm long, forming sub-parallel and and thomsonite-Ca). Calcite occurs in various habits. divergent aggregates (Fig. 2). Crystals are flattened on White spheres composed of curved zeophyllite crystals {10¯1}, and elongated on [101], with the crystal forms: also occur frequently. Ettringite, sometimes partially {010}, {10¯1} and {111} (Fig. 3). Crystals are transpar- transformed into thaumasite, can be found. The quarry ent with a vitreous luster. The mineral has a yellow is the type locality for brenkite (Hentschel et al. 1978). streak. Vandermeerscheite is non-fluorescent under Fluorite occurs as greyish worm-like aggregates. Van- both long- and short-wavelength ultraviolet radiation. dermeerscheite was found in the cavities growing on The Mohs hardness is about 2. Crystals are brittle with perfect cleavage on {10¯1} and have curved fracture. The calculated density is 4.502 g·cm–3 based on the empirical formula; 4.507 g·cm–3 for the ideal formula. Vandermeerscheite dissolves easily in dilute HCl at room temperature. Optically, vandermeerscheite is biaxial (–), with α = 1.83 (calc.), β = 1.90(1), γ = 1.91(1) (measured in white light at 22 °C). The measured 2V is 40(10)° estimated from conoscopic observations of the interference figure; dispersion is moderate r < v. No pleochroism was ob- served. Optical orientation is X ≈ {10¯1}, Y ≈ [101], Z = b. Note that X is perpendicular to the thin direction of the tiny blades, making α impossible⊥ to measure; con- sequently, it was calculated from β, γ and 2V. Fig. 1 Vandermeerscheite crystals on “phillipsite–K”. Cotype specimen. Width of the photograph is 0.8 mm. Fig. 2 Typical rosette-like aggregate of vandermeerscheite crystals on “phillipsite–K” crystals. Back-scattered electron image (photo by E. Van Fig. 3 Crystal drawing of vandermeerscheite; clinographic projection Der Meersche and Herman Goethals). in nonstandard orientation, [101] vertical. 220 Vandermeerscheite, a new uranyl vanadate Tab. 1 Chemical composition (in wt. %) for vandermeerscheite utilizing a 633 nm laser. Spectral calibration was done Constituent Mean Range Stand. Dev. Probe Standard on Ne-emission lines using a low-pressure Ne-discharge lamp. Na2O 0.13 0.01–0.26 0.08 albite There were no bands of significant intensities ob- K2O 9.85 8.99–10.26 0.40 sanidine CaO 0.30 0.21–0.43 0.06 fluorapatite served in the region of O–H stretching vibrations. A –1 V2O5 20.30 19.40–20.30 0.61 ScVO4 very weak band at 1605 cm may be assignable to the UO3 64.41 61.79–66.41 1.49 parsonsite ν2 (δ) H–O–H bending vibration of H2O and those at –1 H2O* 4.04 1463 and 1072 cm are most probably overtones or Total 99.03 combination bands. A medium strong band at 970 cm–1 * as determined from crystal structure is attributed to the ν1 VO3 symmetric stretching vibra- tion of V2O8 dimers. Similar bands were observed in the 4. Chemical composition spectra of carnotite (975 cm–1) and francevillite (976 cm–1) (Frost et al. 2005). A medium strong band at 820 A crystal aggregate of vandermeerscheite crystals was –1 2+ cm is attributed to the ν1 UO2 symmetric stretching analyzed (Tab. 1) using a Cameca SX100 electron mi- vibration. Some bands in the Raman spectrum of car- croprobe (Masaryk University, Brno), operating in WDS notite and francevillite (Frost et al. 2005) observed in mode with an accelerating voltage of 15 kV, beam cur- –1 the range from 950 to 850 cm were assigned to the ν3 rent of 2 nA, and a 5 µm beam diameter. The following 2+ UO2 antisymmetric stretching vibrations; however, X-ray lines and standards were used: Kα lines: Na (al- this IR-active vibration remains Raman inactive in bite), K (sanidine), Ca (fluorapatite), V (synth. ScVO4); the case of vandermeerscheite. The U–O bond length M line: U (parsonsite). Other likely elements, such as Si, 2+ α in uranyl inferred from the ν1 UO2 is approximately Al, S, P, K, V and F were also sought, but their contents 1.79 Å (Bartlett and Cooney 1989). This value is in were below the detection limits (~0.05–0.15 wt. % with line with that obtained from the structure (1.77 Å) the analytical conditions used).