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Extending the mineralogy of U6+ (II): Barronite, a new uranyl silicate related to weeksite from Menzenschwand, Germany
Published online by Cambridge University Press: 07 July 2025
Abstract
The new mineral barronite (IMA 2024-053), (□1.5Ba0.5)2(UO2)2Si5O12(OH)·2H2O, was found in the material from the Menzenschwand uranium deposit, Black Forest Mts., Germany, where it occurs as globular/acicular aggregates, consisting of long-prismatic crystals, up to 0.3 mm in length, in baryte and quartz-based gangue. Barronite is not associated with any other supergene minerals. Crystals are pale yellow with a colourless to pale yellow streak. Nevertheless, some of the crystals have a brown-orange tint, caused by Fe–Si-gels. The tenacity is brittle, the Mohs hardness is 1–2. The mineral has distinct cleavage on {100}; the fracture is uneven. Barronite is biaxial (+), with α = 1.599(2), β = 1.607(2), γ = 1.617(3); and 2V (meas.) = 86°. Optical orientation is X = b, Y ˄ a ≈ 3° in the obtuse angle β. Dispersion is distinct r>v. Pleochroism is distinct in hues of pale yellow, X<Y<Z. Electron microprobe analyses provided (based on 19 O atoms) (□1.369Ba0.345K0.165Ca0.086Pb0.024Fe0.011)Σ2.000(U0.996O2)2Si4.989O12(OH)·2H2O. Barronite is monoclinic, C2/m, a = 14.2115(11) Å, b = 14.0169(19) Å, c = 9.6545(8) Å, β = 111.59(6)°, with V = 1788.2(8) Å3 (Z = 4), refined from the corrected 3D ED data at 94K. The crystal structure refinement (R1 = 0.0791 for 6596 [I > 3σ(I)] reflections) refined from the 3D ED data confirmed that barronite has the same structural architecture as weeksite; however, it contains less H2O in the channels of the uranyl-silicate framework structure.
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- © The Author(s), 2025. Published by Cambridge University Press on behalf of The Mineralogical Society of the United Kingdom and Ireland.
Footnotes
Associate Editor: Daniel Atencio
We dedicate this paper to the memory of Prof. Kurt Walenta (1927–2021), who was born in Prague (CZ) and later on made a significant contribution to the mineralogy of uranium.
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