Stuart J. Mills^1,*, Fabrizio Nestola², Volker Kahlenberg³, Andrew G. Christy⁴, Clivia Hejny³ and Günther J. Redhammer⁵

¹Geosciences, Museum Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia
²Dipartimento di Geoscienze, Università di Padova, Via Gradenigo 6, Padova I-35131, Italy
³Institut für Mineralogie und Petrographie der Universität Innsbruck, Innrain 52, 6020 Innsbruck, Austria
⁴Centre for Advanced Microscopy, Australian Natioanl University, Canberra, ACT 0200, Australia
⁵Department of Materials Engineering and Physics, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria

Single-crystal diffraction of jarosite, KFe₃³⁺(SO₄)₂(OH)₆, has been undertaken at low temperatures that proxy for martian surface conditions. Room-temperature data are consistent with literature data [a = 7.2913(5), c = 17.1744(17), and V = 790.72(11) in R3̄m], while the first low-temperature data for the mineral is presented (at 253, 213, 173, and 133 K). Data collections between 297 and 133 K show strongly anisotropic thermal expansion, with the c axis much more expandable than the a axis. Much of the anisotropy is due to strong distortion of the KO₁₂ polyhedron, which increases by 8% between 297 and 133 K. The data sets can aid in the identification of jarosite by X-ray diffraction of martian soils using the Curiosity Rover’s CheMin instrument.

Reference
Mills SJ, Nestola F, Kahlenberg V, Christy AG, Hejny C and Redhammer GJ (2013) Looking for jarosite on Mars: The low-temperature crystal structure of jarosite. American Mineralogist 98:1966-1971.
[doi:10.2138/am.2013.4587]
Copyright: The Mineralogical Society of America

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