Shaunna M. Morrison

Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars

Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.

Curiosity at Gale Crater, Mars: Characterization and Analysis of the Rocknest Sand Shadow

The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles (water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at Mars instrument and of the fine-grained nanophase oxide component first described from basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations.

X-ray diffraction results from mars science laboratory: Mineralogy of rocknest at Gale crater

The Mars Science Laboratory rover Curiosity scooped samples of soil from the Rocknest aeolian bedform in Gale crater. Analysis of the soil with the Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite, and pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite, and ilmenite. The minor phases are present at, or near, detection limits. The soil also contains 27 ± 14 weight percent x-ray amorphous material, likely containing multiple Fe3+- and volatile-bearing phases, including possibly a substance resembling hisingerite. The crystalline component is similar to the normative mineralogy of certain basaltic rocks from Gusev crater on Mars and of martian basaltic meteorites. The amorphous component is similar to that found on Earth in places such as soils on the Mauna Kea volcano, Hawaii.

Mineralogy, provenance, and diagenesis of a potassic basaltic sandstone on Mars: CheMin X-ray diffraction of the Windjana sample (Kimberley area, Gale Crater)

Abstract The Windjana drill sample, a sandstone of the Dillinger member (Kimberley formation, Gale Crater, Mars), was analyzed by CheMin X‐ray diffraction (XRD) in the MSL Curiosity rover. From Rietveld refinements of its XRD pattern, Windjana contains the following: sanidine (21% weight, ~Or95); augite (20%); magnetite (12%); pigeonite; olivine; plagioclase; amorphous and smectitic material (~25%); and percent levels of others including ilmenite, fluorapatite, and bassanite. From mass balance on the Alpha Proton X‐ray Spectrometer (APXS) chemical analysis, the amorphous material is Fe rich with nearly no other cations—like ferrihydrite. The Windjana sample shows little alteration and was likely cemented by its magnetite and ferrihydrite. From ChemCam Laser‐Induced Breakdown Spectrometer (LIBS) chemical analyses, Windjana is representative of the Dillinger and Mount Remarkable members of the Kimberley formation. LIBS data suggest that the Kimberley sediments include at least three chemical components. The most K‐rich targets have 5.6% K2O, ~1.8 times that of Windjana, implying a sediment component with >40% sanidine, e.g., a trachyte. A second component is rich in mafic minerals, with little feldspar (like a shergottite). A third component is richer in plagioclase and in Na2O, and is likely to be basaltic. The K‐rich sediment component is consistent with APXS and ChemCam observations of K‐rich rocks elsewhere in Gale Crater. The source of this sediment component was likely volcanic. The presence of sediment from many igneous sources, in concert with Curiositys identifications of other igneous materials (e.g., mugearite), implies that the northern rim of Gale Crater exposes a diverse igneous complex, at least as diverse as that found in similar‐age terranes on Earth.

Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater

Significance Tridymite, a SiO2 mineral that crystallizes at low pressures and high temperatures (>870 °C) from high-SiO2 materials, was detected at high concentrations in a sedimentary mudstone in Gale crater, Mars. Mineralogy and abundance were determined by X-ray diffraction using the Chemistry and Mineralogy instrument on the Mars Science Laboratory rover Curiosity. Terrestrial tridymite is commonly associated with silicic volcanism where high temperatures and high-silica magmas prevail, so this occurrence is the first in situ mineralogical evidence for martian silicic volcanism. Multistep processes, including high-temperature alteration of silica-rich residues of acid sulfate leaching, are alternate formation pathways for martian tridymite but are less likely. The unexpected discovery of tridymite is further evidence of the complexity of igneous petrogenesis on Mars, with igneous evolution to high-SiO2 compositions. Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ∼40 wt.% crystalline and ∼60 wt.% X-ray amorphous material and a bulk composition with ∼74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (∼17 wt.% of bulk sample), tridymite (∼14 wt.%), sanidine (∼3 wt.%), cation-deficient magnetite (∼3 wt.%), cristobalite (∼2 wt.%), and anhydrite (∼1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (∼39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides−perchlorates−chlorates), and has minor TiO2 and Fe2O3T oxides (∼5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a “Lake Gale” catchment environment can account for Buckskin’s tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill.

The origin and implications of clay minerals from Yellowknife Bay, Gale crater, Mars

Abstract The Mars Science Laboratory (MSL) rover Curiosity has documented a section of fluvio-lacustrine strata at Yellowknife Bay (YKB), an embayment on the floor of Gale crater, approximately 500 m east of the Bradbury landing site. X‑ray diffraction (XRD) data and evolved gas analysis (EGA) data from the CheMin and SAM instruments show that two powdered mudstone samples (named John Klein and Cumberland) drilled from the Sheepbed member of this succession contain up to ~20 wt% clay minerals. A trioctahedral smectite, likely a ferrian saponite, is the only clay mineral phase detected in these samples. Smectites of the two samples exhibit different 001 spacing under the low partial pressures of H2O inside the CheMin instrument (relative humidity <1%). Smectite interlayers in John Klein collapsed sometime between clay mineral formation and the time of analysis to a basal spacing of 10 Å, but largely remain open in the Cumberland sample with a basal spacing of ~13.2 Å. Partial intercalation of Cumberland smectites by metal-hydroxyl groups, a common process in certain pedogenic and lacustrine settings on Earth, is our favored explanation for these differences. The relatively low abundances of olivine and enriched levels of magnetite in the Sheepbed mudstone, when compared with regional basalt compositions derived from orbital data, suggest that clay minerals formed with magnetite in situ via aqueous alteration of olivine. Mass-balance calculations are permissive of such a reaction. Moreover, the Sheepbed mudstone mineral assemblage is consistent with minimal inputs of detrital clay minerals from the crater walls and rim. Early diagenetic fabrics suggest clay mineral formation prior to lithification. Thermodynamic modeling indicates that the production of authigenic magnetite and saponite at surficial temperatures requires a moderate supply of oxidants, allowing circum-neutral pH. The kinetics of olivine alteration suggest the presence of fluids for thousands to hundreds of thousands of years. Mineralogical evidence of the persistence of benign aqueous conditions at YKB for extended periods indicates a potentially habitable environment where life could establish itself. Mediated oxidation of Fe2+ in olivine to Fe3+ in magnetite, and perhaps in smectites provided a potential energy source for organisms.

Ferrian saponite from the Santa Monica Mountains (California, U.S.A., Earth): Characterization as an analog for clay minerals on Mars with application to Yellowknife Bay in Gale Crater

Abstract Ferrian saponite from the eastern Santa Monica Mountain, near Griffith Park (Los Angeles, California), was investigated as a mineralogical analog to smectites discovered on Mars by the CheMin X-ray diffraction instrument onboard the Mars Science Laboratory (MSL) rover. The martian clay minerals occur in sediment of basaltic composition and have 02l diffraction bands peaking at 4.59 Å, consistent with tri-octahedral smectites. The Griffith saponite occurs in basalts as pseudomorphs after olivine and mesostasis glass and as fillings of vesicles and cracks and has 02l diffraction bands at that same position. We obtained chemical compositions (by electron microprobe), X-ray diffraction patterns with a lab version of the CheMin instrument, Mössbauer spectra, and visible and near-IR reflectance (VNIR) spectra on several samples from that locality. The Griffith saponite is magnesian, Mg/(Mg+SFe) = 65-70%, lacks tetrahedral Fe3+ and octahedral Al3+, and has Fe3+/SFe from 64 to 93%. Its chemical composition is consistent with a fully tri-octahedral smectite, but the abundance of Fe3+ gives a nominal excess charge of +1 to +2 per formula unit. The excess charge is likely compensated by substitution of O2- for OH-, causing distortion of octahedral sites as inferred from Mössbauer spectra. We hypothesize that the Griffith saponite was initially deposited with all its iron as Fe2+ and was oxidized later. X‑ray diffraction shows a sharp 001 peak at 15 Å, 00l peaks, and a 02l diffraction band at the same position (4.59 Å) and shape as those of the martian samples, indicating that the martian saponite is not fully oxidized. VNIR spectra of the Griffith saponite show distinct absorptions at 1.40, 1.90, 2.30-2.32, and 2.40 mm, arising from H2O and hydroxyl groups in various settings. The position of the ~2.31 mm spectral feature varies systematically with the redox state of the octahedrally coordinated Fe. This correlation may permit surface oxidation state to be inferred (in some cases) from VNIR spectra of Mars obtained from orbit, and, in any case, ferrian saponite is a viable assignment for spectral detections in the range 2.30-2.32 mm.

Mineralogy of an Active Eolian Sediment from the Namib Dune, Gale Crater, Mars

The Mars Science Laboratory rover, Curiosity, is using a comprehensive scientific payload to explore rocks and soils in Gale crater, Mars. Recent investigations of the Bagnold Dune Field provided the first in situ assessment of an active dune on Mars. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on Curiosity performed quantitative mineralogical analyses of the <150 μm size fraction of the Namib dune at a location called Gobabeb. Gobabeb is dominated by basaltic minerals. Plagioclase, Fo56 olivine, and two Ca-Mg-Fe pyroxenes account for the majority of crystalline phases along with minor magnetite, quartz, hematite, and anhydrite. In addition to the crystalline phases, a minimum ~42 wt % of the Gobabeb sample is X-ray amorphous. Mineralogical analysis of the Gobabeb data set provides insights into the origin(s) and geologic history of the dune material and offers an important opportunity for ground truth of orbital observations. CheMins analysis of the mineralogy and phase chemistry of modern and ancient Gale crater dune fields, together with other measurements by Curiositys science payload, provides new insights into present and past eolian processes on Mars.

The first X-ray diffraction measurements on Mars

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.

Relationships between unit-cell parameters and composition for rock-forming minerals on Earth, Mars, and other extraterrestrial bodies

Abstract Mathematical relationships between unit-cell parameters and chemical composition were developed for selected mineral phases observed with the CheMin X-ray diffractometer onboard the Curiosity rover in Gale crater. This study presents algorithms for estimating the chemical composition of phases based solely on X-ray diffraction data. The mineral systems include plagioclase, alkali feldspar, Mg-Fe-Ca C2/c clinopyroxene, Mg-Fe-Ca P21/c clinopyroxene, Mg-Fe-Ca orthopyroxene, Mg-Fe olivine, magnetite, and other selected spinel oxides, and alunite-jarosite. These methods assume compositions of Na-Ca for plagioclase, K-Na for alkali feldspar, Mg-Fe-Ca for pyroxene, and Mg-Fe for olivine; however, some other minor elements may occur and their impact on measured unit-cell parameters is discussed. These crystal-chemical algorithms can be applied to material of any origin, whether that origin is Earth, Mars, an extraterrestrial body, or a laboratory.