Cation arrangement in a unusual uranium-rich senaite: crystal structure study at 130 K
Armbruster, Thomas; Kunz, Martin
European Journal of Mineralogy Volume 2 Number 2 (1990), p. 163 - 170
published: Apr 17, 1990
manuscript accepted: Nov 21, 1989
manuscript received: Sep 18, 1989
ArtNo. ESP147050202002, Price: 29.00 €
Abstract The crystal structure of a crichtonite-type mineral from Pizzo Cervandone (Italy), Pb0.37Ca0.03Sr0.04 U0.48Al0.07V0.20Zn0.27Mn0.28As0.16Nb0.25Sn0.11Y0.23Fe7.12Ti12.32O38, is refined from X-ray single-crystal data collected at 130 K in space group R3̅with a = 10.439(4), c = 21.091(6) Å. The mineral is a unusual U-rich senaite, in which the twelve-coordinated A site is partly occupied by Pb. U is concentrated at the six-coordinated Ml site. This senaite is composed of two distinct cation arrangements which probably form domains within a common close-packed oxygen array. The majority of the cations are arranged as for crichtonite minerals. A smaller proportion of cations have a new ordering pattern, in which only octahedral sites are occupied. In this new structural sub-unit with the composition M20O39, the A site is occupied by oxygen.