S. J. Chipera

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.

BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: POWDER X-RAY DIFFRACTION ANALYSES

The Clay Minerals Society maintains a repository of Source Clays to provide scientists and researchers with a readily available supply of consistent materials so that research conducted by different groups can be correlated to identical material. These Source Clays include kaolinite, smectite, chlorite, vermiculite, illite, palygorskite and other minerals. As most of the Source Clays are naturally occurring materials, they typically contain minor to significant amounts of other mineral impurities. When conducting research using these samples, it is important that their mineral content be well characterized. It is also often desirable to remove these impurities to produce pure clay samples. For example, when studying the biological effects of a particular clay mineral, it is imperative that all contaminants ( e.g. crystalline silica minerals) be removed from the clay in question so that experimental results can be attributed to the clay alone. If purification is required, the clays must be purified in a manner that does not significantly alter the physical or chemical properties of the samples. This chapter describes the X-ray diffraction (XRD) characteristics of a suite of Source Clays of The Clay Minerals Society and demonstrates methods of purification based on Stokes’ law of settling in suspension that can be used to purify the clays. We refer to samples obtained from P. Costanzo (see Costanzo, 2001) as ‘processed’ material and material obtained directly from the Source Clay Repository as ‘as-shipped’ material. Size fractionations and purifi-cations were performed on the ‘as-shipped’ material to obtain the highest purity possible and to identify the impurities that occur in the material. Powder XRD data were collected for the Source Clays on a Siemens D500 powder X-ray diffractometer using CuKα radiation, incident- and diffracted-beam Soller slits, and a Kevex solid-state Si(Li) detector. Data were collected from 2 to 70°2𝛉 using a step size of 0.02°2𝛉 …

Analysis and performance of oil well cement with 30 years of CO2 exposure from the SACROC Unit, West Texas, USA

Abstract A core sample including casing, cement, and shale caprock was obtained from a 30-year old CO2-flooding operation at the SACROC Unit, located in West Texas. The core was investigated as part of a program to evaluate the integrity of Portland-cement based wellbore systems in CO2-sequestration environments. The recovered cement had air permeabilities in the tenth of a milliDarcy range and thus retained its capacity to prevent significant flow of CO2. There was evidence, however, for CO2 migration along both the casing–cement and cement–shale interfaces. A 0.1–0.3 cm thick carbonate precipitate occurs adjacent to the casing. The CO2 producing this deposit may have traveled up the casing wall or may have infiltrated through the casing threads or points of corrosion. The cement in contact with the shale (0.1–1 cm thick) was heavily carbonated to an assemblage of calcite, aragonite, vaterite, and amorphous alumino-silica residue and was transformed to a distinctive orange color. The CO2 causing this reaction originated by migration along the cement–shale interface where the presence of shale fragments (filter cake) may have provided a fluid pathway. The integrity of the casing–cement and cement–shale interfaces appears to be the most important issue in the performance of wellbore systems in a CO2 sequestration reservoir.

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.

Magnesium sulphate salts and the history of water on Mars

Recent reports of ∼30 wt% of sulphate within saline sediments on Mars—probably occurring in hydrated form—suggest a role for sulphates in accounting for equatorial H2O observed in a global survey by the Odyssey spacecraft. Among salt hydrates likely to be present, those of the MgSO4·nH2O series have many hydration states. Here we report the exposure of several of these phases to varied temperature, pressure and humidity to constrain their possible H2O contents under martian surface conditions. We found that crystalline structure and H2O content are dependent on temperature–pressure history, that an amorphous hydrated phase with slow dehydration kinetics forms at <1% relative humidity, and that equilibrium calculations may not reflect the true H2O-bearing potential of martian soils. Mg sulphate salts can retain sufficient H2O to explain a portion of the Odyssey observations. Because phases in the MgSO4·nH2O system are sensitive to temperature and humidity, they can reveal much about the history of water on Mars. However, their ease of transformation implies that salt hydrates collected on Mars will not be returned to Earth unmodified, and that accurate in situ analysis is imperative.

FULLPAT: a full-pattern quantitative analysis program for X-ray powder diffraction using measured and calculated patterns

FULLPAT is a quantitative X-ray diffraction methodology that merges the advantages of existing full-pattern fitting methods with the traditional reference intensity ratio (RIR) method. Like the Rietveld quantitative analysis method, it uses complete diffraction patterns, including the background. However, FULLPAT can explicitly analyze all phases in a sample, including partially ordered or amorphous phases such as glasses, clay minerals, or polymers. Addition of an internal standard to both library standards and unknown samples eliminates instrumental and matrix effects and allows unconstrained analyses to be conducted by direct fitting of library standard patterns to each phase in the sample. Standard patterns may include data for any solid material including glasses, and calculated patterns may also be used. A combination of standard patterns is fitted to observed patterns using least-squares minimization, thereby reducing user intervention and bias. FULLPAT has been coded into Microsoft EXCEL using standard spreadsheet functions.

Stability of hydrous minerals on the martian surface

The presence of water-bearing minerals on Mars has long been discussed, but little or no data exist showing that minerals such as smectites and zeolites may be present on the surface in a hydrated state (i.e., that they could contain H 2O molecules in their interlayer or extraframework sites, respectively). We have analyzed experimental thermodynamic and X-ray powder diffraction data for smectite and the most common terrestrial zeolite, clinoptilolite, to evaluate the state of hydration of these minerals under martian surface conditions. Thermodynamic data for clinoptilolite show that water molecules in its extra-framework sites are held very strongly, with enthalpies of dehydration for Ca-clinoptilolite up to three times greater than that for liquid water. Using these data, we calculated the Gibbs free energy of hydration of clinoptilolite and smectite as a function of temperature and pressure. The calculations demonstrate that these minerals would indeed be hydrated under the very low-P (H2O) conditions existing on Mars, a reflection of their high affinities for H 2O. These calculations assuming the partial pressure of H2O and the temperature range expected on Mars suggest that, if present on the surface, zeolites and Ca-smectites could also play a role in affecting the diurnal variations in martian atmospheric H 2O because their calculated water contents vary considerably over daily martian temperature ranges. The open crystal structure of clinoptilolite and existing hydration and kinetic data suggest that hydration/dehydration are not kinetically limited. Based on these calculations, it is possible that hydrated zeolites and clay minerals may explain some of the recent observations of significant amounts of hydrogen not attributable to water ice at martian mid-latitudes.

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.

Transformations of Mg- and Ca-sulfate hydrates in mars regolith

Abstract Salt hydrates have an active role in regolith development on Mars. The Mg-sulfate system, with highly variable values of n in the formula MgSO4·nH2O, is particularly subject to transformations among several crystalline and amorphous forms. The Ca-sulfate system, CaSO4·nH2O, is likely to be associated with the Mg-sulfates in most occurrences, but is less susceptible to transformations in n. Desiccation of MgSO4·nH2O occurs in exposed soils at the martian equator in summer where higher daytime temperatures at low relative humidity prevail against sluggish nighttime rehydration at high relative humidity. Desiccation and rehydration are both accelerated in the finest size fractions, particularly in silt-size aeolian particles subject to global redistribution by dust storms. This redistribution and periodic excursions into long-term episodes of high obliquity work to rehydrate desiccated MgSO4·nH2O to form epsomite, MgSO4·7H2O, at higher latitudes in the first case and more globally in the latter. Kieserite, a monohydrate form of MgSO4·nH2O resistant to desiccation, can survive equatorial summer conditions, but not protracted high relative humidity; preservation of kieserite at the surface may place limits on the equatorial distribution of ice during past episodes of high obliquity. Deeper horizons in equatorial regolith may preserve hydrated phases through repeated obliquity episodes, raising the possibility of an ancient regolith archive of past hydration. At shallower depths in the regolith, in situ determination of the hydration states of the Mg-sulfates, and possibly the Ca-sulfates, may be used to constrain regolith dynamics if rates and modes of transitions in n can be fully characterized.