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      The first X-ray diffraction measurements on Mars

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          Abstract

          The X-ray diffraction/X-ray fluorescence instrument CheMin on the Curiosity rover is a shoebox-sized device using transmission geometry and an energy-discriminating CCD detector. The instrument has returned the first X-ray diffraction data for soil and drilled samples from Mars outcrops, revealing a suite of primary basaltic minerals, amorphous components and varied hydrous alteration products including phyllosilicates.

          Abstract

          The Mars Science Laboratory landed in Gale crater on Mars in August 2012, and the Curiosity rover then began field studies on its drive toward Mount Sharp, a central peak made of ancient sediments. CheMin is one of ten instruments on or inside the rover, all designed to provide detailed information on the rocks, soils and atmosphere in this region. CheMin is a miniaturized X-ray diffraction/X-ray fluorescence (XRD/XRF) instrument that uses transmission geometry with an energy-discriminating CCD detector. CheMin uses onboard standards for XRD and XRF calibration, and beryl:quartz mixtures constitute the primary XRD standards. Four samples have been analysed by CheMin, namely a soil sample, two samples drilled from mudstones and a sample drilled from a sandstone. Rietveld and full-pattern analysis of the XRD data reveal a complex mineralogy, with contributions from parent igneous rocks, amorphous components and several minerals relating to aqueous alteration. In particular, the mudstone samples all contain one or more phyllosilicates consistent with alteration in liquid water. In addition to quantitative mineralogy, Rietveld refinements also provide unit-cell parameters for the major phases, which can be used to infer the chemical compositions of individual minerals and, by difference, the composition of the amorphous component.

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          Most cited references 14

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          Two-dimensional detector software: From real detector to idealised image or two-theta scan

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            A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale crater, Mars.

            The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.
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              GSAS-II: the genesis of a modern open-source all purpose crystallography software package

              The newly developedGSAS-IIsoftware is a general purpose package for data reduction, structure solution and structure refinement that can be used with both single-crystal and powder diffraction data from both neutron and X-ray sources, including laboratory and synchrotron sources, collected on both two- and one-dimensional detectors. It is intended thatGSAS-IIwill eventually replace both theGSASand theEXPGUIpackages, as well as many other utilities.GSAS-IIis open source and is written largely in object-oriented Python but offers speeds comparable to compiled code because of its reliance on the Python NumPy and SciPy packages for computation. It runs on all common computer platforms and offers highly integrated graphics, both for a user interface and for interpretation of parameters. The package can be applied to all stages of crystallographic analysis for constant-wavelength X-ray and neutron data. Plans for considerable additional development are discussed.
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                Author and article information

                Journal
                IUCrJ
                IUCrJ
                IUCrJ
                IUCrJ
                International Union of Crystallography
                2052-2525
                01 November 2014
                21 October 2014
                21 October 2014
                : 1
                : Pt 6 ( publisher-idID: m140600 )
                : 514-522
                Affiliations
                [a ]Geological Sciences, Indiana University, 1001 E. 10th Street, Bloomington, IN 47405, USA
                [b ]NASA Ames Research Center, USA
                [c ]Planetary Science Institute, USA
                [d ]inXitu, USA
                [e ]University of Hawaii at Manoa, USA
                [f ]Chesapeake Energy, USA
                [g ]NASA Jet Propulsion Laboratory, USA
                [h ]University of Arizona, USA
                [i ]Arizona State University, USA
                [j ]CNRS, France
                [k ]NASA Johnson Space Center, USA
                [l ]Lunar and Planetary Institute, USA
                Author notes
                Correspondence e-mail: bish@ 123456indiana.edu
                Article
                yu5005 IUCRAJ S2052252514021150
                10.1107/S2052252514021150
                4224469
                25485131
                © David Bish et al. 2014

                This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

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