For the first time on Mars, the crystalline magnesium‐sulfate mineral starkeyite (MgSO 4 ‧4H 2 O) was definitively identified using the CheMin X‐ray diffraction instrument at Gale crater. At the Canaima drill site, starkeyite along with amorphous MgSO 4 ‧ n H 2 O are among the “polyhydrated Mg‐sulfates” interpreted in orbital reflectance spectra. Mg‐sulfates are good climate indicators as they are very responsive to changes in temperature and relative humidity. We hypothesize that, through evaporation, Mg‐sulfates formed at the end of brine evolution when ion concentrations became saturated and precipitated on the surface or near sub‐surface as either epsomite or meridianiite. These minerals were subsequently dehydrated later to starkeyite and amorphous MgSO 4 ‧ n H 2 O in response to a drier Mars. At Canaima, starkeyite is stable and would form during the warmer Mars summers. Due to very slow kinetics at the low Mars winter temperatures, starkeyite and amorphous MgSO 4 ‧ n H 2 O would be resistant to recrystallize to more hydrous forms and thus likely persist year‐round. During the course of analyses, starkeyite transforms into amorphous MgSO 4 ‧ n H 2 O inside the rover body due to the elevated temperature and greatly reduced relative humidity compared to the martian surface at the Canaima drill site. It is possible that crystalline sulfate minerals existed in earlier samples measured by CheMin but altered inside the rover before they could be analyzed. Starkeyite is most likely prevalent in the subsurface, whereas both starkeyite and amorphous MgSO 4 ‧ n H 2 O are likely present on the surface as starkeyite could partially transform into amorphous MgSO 4 ‧ n H 2 O due to direct solar heating.

The Glen Torridon (GT) region in Gale crater, Mars is a region with strong clay mineral signatures inferred from orbital spectroscopy. The CheMin X‐ray diffraction (XRD) instrument onboard the Mars Science Laboratory rover, Curiosity , measured some of the highest clay mineral abundances to date within GT, complementing the orbital detections. GT may also be unique because in the XRD patterns of some samples, CheMin identified new phases, including: (a) Fe‐carbonates, and (b) a phase with a novel peak at 9.2 Å. Fe‐carbonates have been previously suggested from other instruments onboard, but this is the first definitive reporting by CheMin of Fe‐carbonate. This new phase with a 9.2 Å reflection has never been observed in Gale crater and may be a new mineral for Mars, but discrete identification still remains enigmatic because no single phase on Earth is able to account for all of the GT mineralogical, geochemical, and sedimentological constraints. Here, we modeled XRD profiles and propose an interstratified clay mineral, specifically greenalite‐minnesotaite, as a reasonable candidate. The coexistence of Fe‐carbonate and Fe‐rich clay minerals in the GT samples supports a conceptual model of a lacustrine groundwater mixing environment. Groundwater interaction with percolating lake waters in the sediments is common in terrestrial lacustrine settings, and the diffusion of two distinct water bodies within the subsurface can create a geochemical gradient and unique mineral front in the sediments. Ultimately, the proximity to this mixing zone may have controlled the secondary minerals preserved in sedimentary rocks exposed in GT.

Modified clay minerals on Mars Sedimentary rocks exposed in Gale crater on Mars contain extensive clay minerals. Bristow et al. analyzed drill samples collected by the Curiosity rover as it climbed up sedimentary layers in the crater. They found evidence of past reactions with liquid water and sulfate brines, which could have percolated through the clay from an overlying sulfate deposit. Similar sulfate deposits are widespread across the planet and represent some of the last sedimentary rocks to form before the planet lost its surface liquid water, so the results inform our understanding of the geologic processes that occurred as Mars dried out. Science, abg5449, this issue p. 198

MATERIALS IDENTIFIED IN SEDIMENTARY DEPOSITS AT GALE CRATER, MARS C. N. Achilles, R. V. Morris, E. B. Rampe, T. S. J. Gabriel, D. W. Ming, B. Sutter, S. J. Chipera, D. F. Blake, T. F. Bristow, A. C. McAdam, R. T. Downs, D. T. Vaniman, A. S. Yen, NASA GSFC (cherie.n.achilles@nasa.gov), NASA JSC, Arizona State Univ., Jacobs Technology/NASA JSC, Chesapeake Energy, NASA Ames, Univ. of Arizona, Planetary Science Institute, JPL/Caltech.

CRATER, MARS. M. T. Thorpe1*, T. F. Bristow2, E. B. Rampe1, J. P. Grotzinger3, V. K. Fox3, K. A. Bennett4, A. B. Bryk5 A. S. Yen6, A. R. Vasavada6, D. T Vaniman7, V. Tu1, A. H. Treiman8, S. M. Morrison9, D. W. Ming1, R. V. Morris1, A.C. McAdam10, C.A. Malespin11, P. R. Mahaffy10, R. M. Hazen9, S. Gupta11, R. T. Downs12, G. W. Downs12, D. J. DesMarais2, P. I. Craig7, S. J. Chipera7, N. Castle8, D. F. Blake2, and C. N. Achilles10, 1NASA JSC, Houston (michael.t.thorpe@nasa.gov), TX, 2NASA Ames Research Center, 3Caltech, 4USGS, 5Univ. California, Berkeley, 6JPL/Caltech, 7PSI, 8LPI, 9Carnegie Institute, 10NASA GSFC, 11Imperial College, 12Univ. Arizona.

In Situ Crystallographic Investigations of Solar System Objects in the next Decade The Case for In Situ Crystallographic Investigations and InstrumentsThe history of solid solar system materials, whether planetary bodies, planetary satellites, or icy or rocky planetesimals, is written in the rocks and the minerals they contain.Minerals provide the most persistent, accessible, and information-rich record of the origin(s) and evolution of solar system objects, because minerals are stable under a wide range of pressure, temperature, and composition (PTX).Regolith material comprised of specific minerals can be used to identify the conditions under which it formed, as well as subsequent environmental changes, based on individual mineral stability ranges, complex mineral assemblages, and the presence or absence of equilibrium among them.More than elemental, isotopic or optical analysis, definitive and quantitative mineralogical analysis with X-ray Diffraction (XRD) is a direct and unambiguous crystallographic technique.Fully quantitative mineralogical results are obtained from XRD patterns using Rietveld refinement and other full-pattern fitting techniques [1][2][3].XRD provides detailed information about history, environment, and habitability: Past and present climates, the changing activity of water, and the availability and chemical state of biologically significant elements, all through the lens of deep time.Such quantitative mineralogical determinations are not possible if the complete mineral assemblage is not characterized.Chemical, optical, calorimetric or oxidation state data are seldom definitive because any particular chemical compositions, optical emission/absorption features, calorimetric data or valence information can still represent a range of substances or mineral assemblages.Mineral "species" are defined as naturally occurring crystalline thermodynamic phases that have a unique combination of atomic structure and chemical composition.More than 5,500 different mineral species have been described on Earth and their crystallographic structures and other characteristics are tabulated in the open-access ICDD and RRUFF databases [4-5] among others.In addition, about 400,000 crystalline inorganic compounds have been characterized and would be classified as minerals if they were found in the natural environment.Statistical studies reveal that thousands of minerals are as yet undiscovered on Earth and throughout the Solar System [6][7].If an unknown phase (or an inorganic compound not found as a mineral on Earth) is identified by itself or in a simple association, it can be fully characterized (both structure and composition), and its significance to the geologic history of its parent body understood by XRD because, as a crystallographic technique, XRD relies on first principles of symmetry and atomic arrangement for its determinations.The comprehensive, detailed characterization of the mineralogy of any solar system body is fundamental to understanding its origins and evolution."Mineral evolution," the study of the diversity and distribution of minerals through deep time [8][9], reveals that planets and moons experience a sequence of mineralogical stages, each a response to varying physical, chemical, and (in the case of Earth) biological processes.Minerals provide the most robust testimony for such critical aspects of planetary evolution as the differentiation of core, mantle, and crust; the establishment of a geodynamo; the nature and extent of volcanism; the initiation of plate tectonics; the presence and dynamic history of a hydrosphere; the evolution of the atmosphere; and the origin and evolution of a biosphere.Only minerals can preserve such history over billions of years.Only with a comprehensive documentation of mineral species, including detailed information on their structural states and compositional idiosyncrasies by XRD, can we hope to fully document that rich history.

Introduction. Crystalline Ca-sulfate minerals (gypsum CaSO42H2O; bassanite CaSO40.5H2O; and anhydrite CaSO4) were detected in most X-ray diffraction patterns acquired to date by the CheMin transmission XRD instrument [1] onboard the Mars Science Laboratory (MSL) rover Curiosity during its ongoing mission at Gale crater [e.g., 2-10]. Relative proportions of Ca-sulfate minerals vary from sample-tosample and, in some case, vary during multi-sol CheMin analyses in response to different environmental conditions in situ and within the CheMin instrument [11]. Chemical associations of Ca and S are prevalent at Gale crater, particularly in Ca-sulfate-rich veins that penetrate local sedimentary rock [e.g., 12-14]. No other crystalline monocation sulfates or their hydrated equivalents (e.g., MgSO4⋅nH2O) have yet been detected by CheMin though chemical associations (e.g., Mg and S) are present [e.g., 12-14]. No detection of crystalline monocation sulfates by CheMin, excepting Ca-sulfates, implies other monocation sulfates (e.g., MgSO4, MnSO4, FeSO4, and Fe2(SO4)3 and hydrated equivalents) are present below CheMin detection limits, are XRD amorphous [e.g., 1518], or were not sampled. We advance here a pathway for precipitation of crystalline Ca-sulfates and amorphous Mg-sulfate based on experimental evidence for replacement of Ca interlayer cations in smectite SWa-1 by Mg sourced from Mg sulfate solutions. Samples and Methods. Clay Mineral Society smectite SWa-1 was purified as a <0.5 μm size fraction by grinding, sonic probe disaggregation, Stokes-Law settling in deionized water, and centrifuging and washing multiple times with deionized water. Air dried purified powder is referred to here as SWa1_ORIG. A 1.0 g portion was combined with 10 g of Ca-free, 0.05 M MgSO4 reagent solution, and resulting the suspension was agitated on a shaker arm at ~25 °C for 21 d. After agitation, a split was air dried (SWa1_EVAP), and remaining sample subjected to two centrifuge (8000 rpm for ~40 min), decant, and wash cycles with deionized water (no intervening drying) before air-drying (SWa1_WASH). Samples were analyzed by XRD (Siemens D500 at LANL and CheMin-4 (CM4) at JSC), VNIR reflectance spectroscopy (ASD FieldSpec3 at JSC) in air or N2 purged glove box (25°C; RH~0.4%), thermogravametric (TG) analysis (Netzsch STA F1 Jupiter coupled to Pfeiffer QMS at JSC; He/1000mbar/3sccm), and XRF (Rigaku ZSX at LANL). VNIR peak positions were determined from continuum-removed spectra. Results and Discussion. The SWa1_ORIG XRD pattern (Fig. 1) is typical for ferric dioctahedral smectites with 001 reflections at 15.2 Å in air and 13.6 Å in dry N2 and at 02L reflections at 4.50 Å for both atmospheres. The smectite pattern is invariant across all three samples, and gypsum peaks are present only for SWa1_EVAP.

In August 2015, the Curiosity Mars rover discovered tridymite, a high‐temperature silica polymorph, in Gale crater. The existing model for its occurrence suggests erosion and detrital sedimentation from silicic volcanic rocks in the crater rim or central peak. The chemistry and mineralogy of the tridymite‐bearing rocks, however, are not consistent with silicic volcanic material. Using data from Curiosity, including chemical composition from the Alpha Particle X‐ray Spectrometer, mineralogy from the CheMin instrument, and evolved gas and isotopic analyses from the Sample Analysis at Mars instrument, we show that the tridymite‐bearing rocks exhibit similar chemical patterns with silica‐rich alteration halos which crosscut the stratigraphy. We infer that the tridymite formed in‐place through hydrothermal processes and show additional chemical and mineralogical results from Gale crater consistent with hydrothermal activity occurring after sediment deposition and lithification.

Siderite (FeCO3) has been detected in Gale Crater for the first time by the Mars Science Laboratory (MSL) Curiosity and is seen in multiple samples in the Glen Torridon (GT) region. The identification of siderite is based on evolved gas analysis (EGA) data from the Sample Analysis at Mars (SAM) instrument and X-ray diffraction (XRD) data from the Chemistry and Mineralogy (CheMin) instrument. Curiosity descended off of the Vera Rubin ridge (VRR) into the Glen Torridon region on Sol 2300. Glen Torridon is of particular interest because a strong clay mineral signature had been detected by orbital instruments [1]. To date, four drilled samples have been collected at two different drill locations: Kilmarie and Aberlady from adjacent blocks at the base of the south side of VRR in the Jura member and Glen Etive 1 and 2 on the same block in the Knockfarril member.

Vera Rubin ridge (VRR) is an erosion-resistant feature on the northwestern slope of Mount Sharp in Gale crater, Mars, and orbital visible/shortwave infrared measurements indicate it contains red hematite. The Mars Science LaboratoryCuriosityrover performed an extensive campaign on VRR to study its mineralogy, geochemistry, and sedimentology to determine the depositional and diagenetic history of the ridge and constrain the processes by which the hematite could have formed. X-ray diffraction (XRD) data from the CheMin instrument of four samples drilled on and below VRR demonstrate differences in iron, phyllosilicate, and sulfate mineralogy and hematite grain size. Hematite is common across the ridge, and its detection in a gray outcrop suggest localized regions with coarse-grained hematite, which commonly forms from warm fluids. Broad XRD peaks for hematite in one sample below VRR and the abundance of FeO(T)in the amorphous component suggest the presence of nanocrystalline hematite and amorphous Fe oxides/oxyhydroxides. Well crystalline akaganeite and jarosite are present in two samples drilled from VRR, indicating at least limited alteration by acid-saline fluids. Collapsed nontronite is present below VRR, but samples from VRR contain phyllosilicate with d(001) = 9.6 angstrom, possibly from ferripyrophyllite or an acid-altered smectite. The most likely cementing agents creating the ridge are hematite and opaline silica. We hypothesize late diagenesis can explain much of the mineralogical variation on the ridge, where multiple fluid episodes with variable pH, salinity, and temperature altered the rocks, causing the precipitation and crystallization of phases that are not otherwise in equilibrium.

Clay minerals are common in ancient terrains on Mars and their presence at the surface alludes to aqueous processes in the Noachian to Early Hesperian (>3.5 Ga). Gale crater was selected as Curiosity’s landing site largely because of the identification of clay mineral rich strata from orbit. On Earth, the types of clay minerals (i.e., smectites) identified in Gale crater are typically juvenile weathering products that ultimately record the interaction between primary igneous minerals with the hydrosphere, atmosphere, and biosphere. Trioctahedral and dioctahedral smectite were identified by Curiosity in units stratigraphically below the Clay Mineral-Bearing Unit (CBU) identified from orbit. Compositional and sedimentological data suggest the smectite formed via authigenesis in a lake environment and may have been altered during early diagenesis. The CBU is stratigraphically equivalent to a hematite-rich unit to the north and stratigraphically underlies sulfate-rich units to the south, suggesting a dynamic environment and evolving history of water in the ancient Gale crater lake. Targeting these clay mineral rich areas on Mars with rover missions provides an opportunity to explore the aqueous and sedimentary history of the planet.

The Curiosity rover's exploration of rocks and soils in Gale crater has provided diverse geochemical and mineralogical data sets, underscoring the complex geological history of the region. We report the crystalline, clay mineral, and amorphous phase distributions of four Gale crater rocks from an 80-m stratigraphic interval. The mineralogy of the four samples is strongly influenced by aqueous alteration processes, including variations in water chemistries, redox, pH, and temperature. Localized hydrothermal events are evidenced by gray hematite and maturation of amorphous SiO2 to opal-CT. Low-temperature diagenetic events are associated with fluctuating lake levels, evaporative events, and groundwater infiltration. Among all mudstones analyzed in Gale crater, the diversity in diagenetic processes is primarily captured by the mineralogy and X-ray amorphous chemistry of the drilled rocks. Variations indicate a transition from magnetite to hematite and an increase in matrix-associated sulfates suggesting intensifying influence from oxic, diagenetic fluids upsection. Furthermore, diagenetic fluid pathways are shown to be strongly affected by unconformities and sedimentary transitions, as evidenced by the intensity of alteration inferred from the mineralogy of sediments sampled adjacent to stratigraphic contacts.

Martian fluids and their evaporation products – an overview using thermochemical modelling Conference or Workshop Item How to cite: Schwenzer, Susanne; Bridges, John; Turner, Stuart; Ramkissoon, Nisha; Cogliati, Simone; Seidel, Robert; Reed, Mark; Filiberto, Justin; Vaniman, D. and Olsson-Francis, Karen (2020). Martian fluids and their evaporation products – an overview using thermochemical modelling. In: 51st Lunar and Planetary Science Conference, 16-18 Mar 2020.

S.M. Clegg, J. Frydenvang, R.B. Anderson, D.T. Vaniman, P. Gasda, O. Forni, H. Newsom, D. Blaney, S. Maurice, R.C. Wiens, Los Alamos National Laboratory, Los Alamos, NM, sclegg@lanl.gov, Univ. of Copenhagen, Copenhagen, Denmark, USGS, Flagstaff, AZ, Planetary Science Institute, Tucson, AZ, Institut de Recherches en Astrophysique et Planétologie, Toulouse, France, University of New Mexico, Albuquerque, NM, Jet Propulsion Laboratory, Pasadena, CA,

Hydrothermal high sanidine and specular hematite are found within ferric-rich and gray-colored cemented basaltic breccia occurring within horizontal, weathering-resistant strata exposed in an erosional gully of the Pu'u Poliahu cinder cone in the summit region of Maunakea volcano (Hawai'i). The cone was extensively altered by hydrothermal, acid-sulfate fluids at temperatures up to similar to 400 degrees C, and, within strata, plagioclase was removed by dissolution from progenitor Hawaiitic basalt, and sanidine and hematite were precipitated. Fe2O3T concentration and Fe3+/ n-ary sumation Fe redox state are similar to 12 wt.% and similar to 0.4 for progenitor basalt and 46-60 wt.% and similar to 1.0 for cemented breccias, respectively, implying open-system alteration and oxic precipitation. Hydrothermal high sanidine (adularia) is characterized by full Al,Si structural disorder and monoclinic unit-cell (Rietveld refinement):a = 8.563(19) angstrom, b = 13.040(6) angstrom, c = 7.169(4) angstrom, beta = 116.02(10)degrees, andV = 719.4(19) angstrom(3). Hematite (structure confirmed by Rietveld refinement) is the predominant Fe-bearing phase detected. Coarse size fractions of powdered hematite-rich breccia (500-1000 mu m) are dark and spectrally neutral at visible wavelengths, confirming specular hematite, and SEM images show platy to polyhedral hematite morphologies with longest dimensions >10 mu m. Smectite and 10-angstrom phyllosilicate, both chemically dominated by Mg as octahedral cation, are additional diagenetic hydrothermal alteration products. By analogy and as a working hypothesis, high sanidine (Kimberly formation) and specular hematite (Mt. Sharp group at Hartmann's Valley and Vera Rubin ridge) at Gale crater are interpreted as diagenetic alteration products of Martian basaltic material by hydrothermal processes.