David Vaniman, Steve Chipera, Patricia Craig Calendar Year 2018 I. Report on research For calendar year 2018, focus remained on the Mars Science Laboratory (MSL) mission. Vaniman’s involvement with MSL continued in roles with two instruments, the CheMin X-ray diffraction (XRD) and X-ray florescence (XRF) instrument and, to lesser extent, the ChemCam laser-induced breakdown spectroscopy (LIBS) and remote micro-imager (RMI) instrument. Chipera and Craig are involved with the CheMin instrument. (1) Research at the MSL Gale Crater Field Site on Mars (1a) CheMin Instrument on MSL. David Vaniman is a Co-I on the CheMin instrument for Mars Science Laboratory (MSL); the PI is Tom Bristow of NASA Ames. This report also covers Steve Chipera, who is a Co-I for the CheMin instrument, and Patricia Craig, who is a Postdoctoral Research Scientist for the CheMin team. Steve Chipera works through PSI as a Senior Research Associate for the MSL mission and reports to Dave Vaniman. Patricia Craig, who is a Postdoctoral Research Scientist at PSI, also reports to Dave Vaniman. Vaniman has tactical, data analysis, and Planetary data System (PDS) reporting roles for MSL. Steve Chipera has a data analysis role and Patricia Craig has both tactical and data analysis roles for MSL. As members of the CheMin Science Team tasked with operations, Vaniman’s and Craig’s tactical participation included operations in the role of combined Payload Uplink Lead and Payload Downlink Lead (PUDL). With Dick Morris (NASA-JSC) and Mike Wilson (NASA-Ames), Vaniman completed three additional rounds of data delivery for the Planetary Data System (PDS), one on February 16, 2018 (PDS release #17), one on June 29, 2018 (PDS release #18), and one on November 2, 2018 (PDS release #19). During this reporting period Vaniman, Chipera, and Craig assisted in characterization of Mars samples analyzed by CheMin. New samples collected and analyzed during this period were drill samples form Vera Rubin Ridge (informally known as Hematite Ridge). The three drill samples collected were Duluth, Stoer, and Highfield. Chipera’s expertise was used in application of FULLPAT analysis for quantifying amorphous, poorly crystalline, and clay mineral components in these samples. Vaniman, Chipera and Craig contributed to five research papers that were published during this review period. A paper by Bristow et al. (2018) studied clay minerals at Gale cater with implications for surface chemical weathering, lake levels, and atmospheric infiltration. Two back-to-back papers by Morrison et al. (2018a,b) developed algorithms for obtaining crystal chemistry from X-ray diffraction data (Part 1) and applied these methods to the mineralogy of Gale crater (Part 2). In Rampe et al. (2018) Chemin XRD data and CRISM-based estimates of mineralogy were used to examine variability in mineralogy and mineral sources in eolain dunes encountered on the lower slopes of Mount Sharp. In Vaniman et al. (2018) we reported on gypsum, bassanite and anhydrite at Gale crater and discussed mineral dehydration reactions within CheMin (gypsum dehydration to bassanite); the polyphase Ca-sulfate associations at Gale crater reflect limited opportunities for equilibration and presage mixed salt associations anticipated in higher strata that are more sulfate-rich and may mark local or global environmental change In Bristow et al. (2018), the accumulated clay mineral data for Gale crater was examined for indications of evolution of aqueous conditions and possible habitats. The ~3.5–billion year (Ga) fluvio- lacustrine mudstones in Gale crater contain up to ~28 weight % clay minerals. The paper shows that clay mineral X-ray diffraction and evolved gas analyses have paleoenvironmental significance. While perennial lake mudstones are characterized by Fe-saponite, the stratigraphic intervals associated with episodic lake drying contain Al-rich, Fe3+-bearing dioctahedral smectite. Minor ferripyrophyllite, interpreted as wind- blown detritus, is found in candidate aeolian deposits. Results suggest that dioctahedral smectite formed by near-surface chemical weathering driven by fluctuations in lake level and atmospheric infiltration, a process leading to the redistribution of nutrients and potentially influencing the cycling of gases that help regulate climate. Back-to-back papers by Morrison et al., (2018a,b) address (Part 1, 2018a) general relationships between unit-cell parameters and composition for rock-forming minerals and (Part 2, 2018b) the specific crystal chemistry of martian minerals at Gale crater. In Part 1, mathematical relationships between unit-cell parameters and chemical composition were developed for selected mineral phases. Algorithms were developed for estimating the chemical composition of phases based solely on X-ray diffraction data. The mineral systems studied include plagioclase, alkali feldspar, clinopyroxenes, orthopyroxenes, Mg-Fe olivines, magnetites and other selected spinel oxides, and alunite-jarosite. These methods assume simple compositions of Na-Ca for plagioclase, K-Na for alkali feldspar, Mg-Fe-Ca for pyroxene, and Mg-Fe for olivine; however, some minor elements may occur and their impact on measured unit-cell parameters is discussed. In Part 2, the crystal chemical algorithms of Part 1 were used to estimate the chemical composition of selected mineral phases observed with the CheMin X-ray diffractometer at Gale crater. The samples in Part 2 include eolian soils (Rocknest and Gobabeb), mudstones of the Yellowknife Bay formation (John Klein and Cumberland) and the Murray formation (Confidence Hills, Mojave2, and Telegraph Peak), as well as the sandstone Windjana and sandstones of the unaltered Stimson formation (Big Sky and Okoruso) and the altered Stimson formation (Greenhorn and Lubango). Compositional ranges for feldspars, pyroxenes, olivines and magnetites are constrained by this study. Rampe et al. (2018) examined active eolian sands near linear dunes encountered during the Bagnold Dunes campaign in Gale crater, using the Ogunquit Beach scoop sample from a large-ripple trough within the Mount Desert Island ripple field. This sand is dominated by basaltic igneous minerals and X-ray amorphous materials. CheMin mineralogy of the prior Gobabeb sample acquired at a large-ripple crest on the Namib barchan dune is similar to Ogunquit Beach. Ogunquit Beach, however, contains more plagioclase and Gobabeb contains more olivine. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)- based estimates of mineralogy at the optical surface of Namib Dune and Mount Desert Island demonstrate that surface sands are enriched in olivine and depleted in plagioclase at Mount Desert Island relative to Namib Dune. Differences between CheMin-derived and CRISM-derived mineralogies suggest sorting by grain size on bedform to dune field scales. Crystal chemistry from CheMin suggests contributions from multiple igneous sources and the local bedrock. In Vaniman et al. (2018) we show that gypsum, bassanite, and anhydrite are common minerals at Gale crater. Warm conditions (~6 to 30 °C) within CheMin drive gypsum dehydration to bassanite; measured surface temperatures and modeled temperature depth profiles indicate that near-equatorial warm-season surface heating can also cause gypsum dehydration to bassanite. By accounting for instrumental dehydration effects we are able to quantify the in situ abundances of Ca-sulfate phases in sedimentary rocks and in eolian sands at Gale crater. All three Ca-sulfate minerals occur together in some sedimentary rocks and their abundances and associations vary stratigraphically. Several Ca-sulfate diagenetic events are indicated. Salinity-driven anhydrite precipitation at temperatures below ~50 °C may be supported by co- occurrence of more soluble salts. An alternative pathway to anhydrite via dehydration might be possible, but if so would likely be limited to warmer near-equatorial dark eolian sands that presently contain only anhydrite. The polyphase Ca-sulfate associations at Gale crater reflect limited opportunities for equilibration, and they presage mixed salt associations anticipated in higher strata that are more sulfate-rich and may mark local or global environmental change. Mineral transformations within CheMin also provide a better understanding of changes that might occur in samples returned from Mars. (1b) ChemCam instrument on MSL ChemCam laser induced breakdown spectroscopy (LIBS) and remote micro-imaging (RMI) continued to be used extensively during 2018. Vaniman is a Co-investigator on the ChemCam instrument on Mars Science Laboratory (MSL); the PI is Roger Wiens of Los Alamos National Laboratory. During 2018, Vaniman ceded management of the weekly ChemCam Geochemistry Working Group to Roger Wiens. By December, Vaniman completed his work with CheCam and is now solely focused on CheMin for the MSL mission. (1c) Mars analog research in New Mexico Vaniman continued to analyze Mars-relevant samples from ash beds in Santa Fe Group sediments of the Española basin, and sulfur-bearing samples of the Valles caldera in New Mexico. These analyses used a Terra X-ray diffraction instrument similar to the CheMin instrument on MSL. The ash beds occur in a setting that may be comparable to that of the Buckskin siliceous sediment sample analyzed by MSL in Gale crater. Samples from the Valles caldera were collected in a study led by Anna Szynkiewicz of the University of Tennessee; the goal of this study is to constrain sulfur cycling between groundwater, rock, stream discharge and precipitation using an approach that has bearing on methods to understand such cycling on Mars. An abstract (Szynkiewicz et al. 2018; see below) was presented at AGU this year, and two papers are in press for publication in 2019 (EPSL). II. Publications Peer-reviewed Publications 2018 Bristow, T.F., E. B. Rampe, C.N. Achilles, D.F. Blake, S.J. Chipera, P. Craig, J.A. Crisp, D.J. Des Marais, R.T. Downs, R. Gellert, J.P. Grotzinger, S. Gupta, R.M. Hazen, B. Horgan, J.V. Hogancamp, N. Mangold, P.R. Mahaffy, A.C. McAdam, D.W. Ming, J.M. Morookian, R.V. Morris, S.M. Morrison, A.H. Treiman, D.T. Vaniman, A.R. Vasavada, and A.S. Yen (2018) Clay mineral diversity and abundance in sedimentary rocks of Gale crater, Mars.