Structural Model of Uramarsite

R. K. Rastsvetaeva^a, G. A. Sidorenko^b, A. G. Ivanova^a, and N. V. Chukanov^c

^a Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninski pr. 59, Moscow, 119333 Russia

e-mail: rast@ns.crys.ras.ru

^b All-Russia Research Institute of Mineral Resources (VIMS), Staromonetny per. 31, Moscow, 109017 Russia

^c Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia

Received August 14, 2007

Abstract—The structural model of uramarsite, a new mineral of the uran-mica family from the Bota–Burum
deposit (South Kazakhstan), is determined using a single-crystal X-ray diffraction analysis. The parameters of
the triclinic unit cell are as follows: a = 7.173(2) Å, b = 7.167(5) Å, c = 9.30(1) Å, = 90.13(7), =90.09(4),
= 89.96(4), and space group P1. The crystal chemical formula of uramarsite is:
(UO₂)₂[AsO₄][PO₄,AsO₄][NH₄][H₃O] · 6H₂O (Z = 1). Uramarsite is the second ammonium-containing mineral
of uranium and an arsenate analogue of uramphite. In the case of uramarsite, the lowering of the symmetry from
tetragonal to triclinic, which is accompanied by a triclinic distortion of the tetragonal unit cell, is apparently
caused by the ordering of the As and P atoms and the NH₄, H₃O, and H₂O groups.

PACS numbers: 91.60.Ed

DOI: 10.1134/S1063774508050076

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