Vandermeerscheite, a new uranyl vanadate related to carnotite, from Eifel, Germany

[摘要] 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 rosettelike aggregates of thin blades up to 50 µm long. Crystals are flattened on {10¯1}, and elongated on [101], with crystalforms {010}, {10¯1} and {111}; crystals are transparent with a vitreous luster. Vandermeerscheite is non-fluorescentunder both long- and short-wavelength ultraviolet radiation. The Mohs hardness is ~2. The calculated density is 4.502g·cm–3 based on the empirical formula; 4.507 g·cm–3 for the ideal formula. Vandermeerscheite dissolves easily in diluteHCl at room temperature. The new mineral is biaxial (–), with α = 1.83 (calc.), β = 1.90(1), γ = 1.91(1) (measured inwhite light at 22 °C). The measured 2V is 40(10)° estimated from conoscopic observation of interference figure; dispersion is moderate r < v. No pleochroism was observed. Optical orientation is X ≈ ⊥ {10¯1}, Y ≈ [101], Z = b. The empirical formula of vandermeerscheite (on the basis of 14 O apfu) is (K1.87Ca0.05Na0.04)Σ1.96[(U1.005O2)2V1.99O8]·2H2O. Ramanspectrum is dominated by the vibrations of UO22+ 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 diffractionlines are [dobs, Å (I, %) (hkl) ]: 7.49 (100) (¯101), 4.147 (22) (020), 3.738 (32) (¯202), 3.616 (20) (¯121), 3.254 (31) (112,121), 3.132 (21) (¯122, 022), 2.989 (41) (211, 013). The crystal structure of vandermeerscheite was refined from thesingle-crystal X-ray data to R = 0.0801 for 644 independent observed reflections, with Iobs > 3σ(I). The structure, whichdiffers from carnotite in symmetry, is based upon uranyl vanadate sheets of francevillite topology; in the interlayer, thereare K+ cations and H2O groups that provide inter-sheet linkage. The new mineral honors Belgian amateur mineralogistand famous mineral photographer Eddy Van Der Meersche, who discovered the new mineral.

[学科分类] 自动化工程

[关键词] vandermeerscheite;uranyl vanadate;new mineral;carnotite group;crystal structure