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    Crystal Chemistry of Martian Minerals

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    Author
    Morrison, Shaunna M.
    Issue Date
    2017
    Keywords
    CheMin
    Crystal chemistry
    Crystallography
    Mars
    Mineralogy
    X-ray diffraction
    Advisor
    Downs, Robert T.
    
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    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Embargo
    Release after 30-Dec-2017
    Abstract
    The NASA Mars Science Laboratory (MSL) rover, Curiosity, began exploring Gale crater, Mars in August, 2012 with the primary goal of assessing the past and present habitability of the martian surface. To meet this goal, Curiosity is equipped with an advanced suite of scientific instruments capable of investigating the geology, geochemistry, and atmospheric conditions on Mars. Among these instruments is the CheMin (Chemistry and Mineralogy) X-ray diffractometer whose function is to identify mineral phases present in sediments and rocks by means of X-ray diffraction (XRD). Characterizing the mineralogical make-up of a rock unit is an important step in determining its geologic history. Primary igneous minerals, such as feldspar, olivine, and pyroxene, give information about parental magmas - their composition, temperature, depth and so on. Secondary alteration minerals, like jarosite or akaganeite, point to distinct weathering or diagenetic processes. As such, understanding the mineral occurrence and abundance in Gale crater provides the MSL team with a robust foundation from which to make geologic interpretations. This dissertation details the methods used to determine the chemical composition of selected mineral phases based solely on XRD patterns from CheMin. Curiosity is equipped with instruments capable of measuring bulk composition of a sample [e.g., APXS (Alpha Particle X-ray Spectrometer)] but has no instrument capable of measuring the composition of a single phase in a multi-phase sample. Therefore, we developed crystal chemical algorithms and calibrations based on refined unit-cell parameters in order to predict mineral phase compositions. We have calculated algorithms for plagioclase, alkali feldspar, Mg-Fe-Ca clinopyroxene, Mg-Fe orthopyroxene, Mg-Fe olivine, Fe-oxide spinel, and alunite-jarosite group minerals. Furthermore, we use the estimated compositions of crystalline material in conjunction with bulk sample chemistry from APXS to estimate of the composition of the X-ray amorphous material present in each of the samples analyzed by CheMin in Gale crater.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Geosciences
    Degree Grantor
    University of Arizona
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