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Uranoclite, a new uranyl chloride mineral from the Blue Lizard mine, San Juan County, Utah, USA

Published online by Cambridge University Press:  31 March 2020

Anthony R. Kampf*
Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA90007, USA
Jakub Plášil
Institute of Physics ASCR, v.v.i., Na Slovance 1999/2, 18221 Prague 8, Czech Republic
Travis A. Olds
Section of Minerals and Earth Sciences, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania15213, USA
Barbara P. Nash
Department of Geology and Geophysics, University of Utah, Salt Lake City, UT84112, USA
Joe Marty
5199 East Silver Oak Road, Salt Lake City, UT84108, USA
*Author for correspondence: Anthony R. Kampf, Email:


The new mineral uranoclite (IMA2020-074), (UO2)2(OH)2Cl2(H2O)4, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as tightly intergrown aggregates of irregular yellow crystals in a secondary assemblage with gypsum. The streak is very pale yellow and the fluorescence is bright green–white under 405 nm ultraviolet light. Crystals are translucent with vitreous lustre. The tenacity is brittle, the Mohs hardness is ~1½, the fracture is irregular. The mineral is soluble in H2O and has a calculated density of 4.038 g⋅cm–3. Electron microprobe analyses provided (UO2)2(OH)2.19Cl1.81(H2O)4. The six strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 8.85(38)(002), 5.340(100)(200, 110), 5.051(63)($\bar{2}$02), 4.421(83)(112, 004, 202), 3.781(38)($\bar{2}$12) and 3.586(57)(014, $\bar{2}$04). Uranoclite is monoclinic, P21/n, a = 10.763(8), b = 6.156(8), c = 17.798(8) Å, β = 95.656(15)°, V = 1173.5(18) Å3 and Z = 4. The structure is the same as that of synthetic (UO2)2(OH)2Cl2(H2O)4 in which the structural unit is a dimer consisting of two pentagonal bipyramids that share an equatorial OH–OH edge. The dimers are linked to one another only by hydrogen bonding. This is the second known uranyl mineral containing essential Cl and the first in which Cl coordinates to U6+.

Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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Associate Editor: Sergey V Krivovichev


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