Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Fe3”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Radiolysis of aqueous solutions of acetic acid in the presence of Na-montmorillonite

The gamma-irradiation of 0.8 mol dm-3 aqueous, oxygen-free acetic acid solutions was investigated in the presence or absence of Na-montmorillonite. H2, CH4, CO, CO2, and several polycarboxylic acids were formed in all systems. The primary characteristics observed in the latter system were: (1) Higher yield of the decomposition of acetic acid; (2) Lower yield of the formation of polycarboxylic acids; (3) No effect on the formation of methane; (4) Higher yield of the formation of carbon dioxide; and (5) The reduction of Fe3+ in the octahedral sites of Na-montmorillonite. A possible reaction scheme was proposed to account for the observed changes. The results are important in understanding heterogeneous processes in radiation catalysis and might be significant to prebiotic chemistry.

Non-NASA Center↗
NASA NTRS1995

Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materials

Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mossbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mossbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mossbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.

NASA Discipline Exobiology↗
NASA NTRS1988

The Sturgeon Falls paleosol and the composition of the atmosphere 1.1 Ga BP

A paleosol is exposed along the north bank of the Sturgeon River, some 25 km SW of Baraga, Michigan. The paleosol was developed on hydrothermally altered Keweenawan basalt and is overlain by the Jacobsville sandstone. Textures, mineralogy, and chemical composition change gradually upwards from unweathered metabasalt, through the paleosol, to the contact of the paleosol with the Jacobsville sandstone. Many of these changes are similar to those in modern soils developed on basaltic rocks. However, K has clearly been added to the paleosol, probably by solutions which had equilibrated with K-feldspar in the Jacobsville sandstone. The Keweenawan basalt was oxidized quite extensively during its conversion to greenstone. During weathering, the remaining Fe2+ was oxidized to Fe3+ and was retained in the paleosol. The composition of the parent greenstone and its change during weathering can be used to define an approximate lower limit to the ratio of the O2 pressure to the CO2 pressure in the atmosphere during the formation of the paleosol [formula: see text]. Free O2 must have been present in the atmosphere 1.1 Ga ago, but its partial pressure could have been 10(3) times lower than in the atmosphere today.

NASA Program Exobiology↗
NASA NTRS2004

Evidence from massive siderite beds for a CO2-rich atmosphere before approximately 1.8 billion years ago

It is generally thought that, in order to compensate for lower solar flux and maintain liquid oceans on the early Earth, methane must have been an important greenhouse gas before approximately 2.2 billion years (Gyr) ago. This is based upon a simple thermodynamic calculation that relates the absence of siderite (FeCO3) in some pre-2.2-Gyr palaeosols to atmospheric CO2 concentrations that would have been too low to have provided the necessary greenhouse effect. Using multi-dimensional thermodynamic analyses and geological evidence, we show here that the absence of siderite in palaeosols does not constrain atmospheric CO2 concentrations. Siderite is absent in many palaeosols (both pre- and post-2.2-Gyr in age) because the O2 concentrations and pH conditions in well-aerated soils have favoured the formation of ferric (Fe3+)-rich minerals, such as goethite, rather than siderite. Siderite, however, has formed throughout geological history in subsurface environments, such as euxinic seas, where anaerobic organisms created H2-rich conditions. The abundance of large, massive siderite-rich beds in pre-1.8-Gyr sedimentary sequences and their carbon isotope ratios indicate that the atmospheric CO2 concentration was more than 100 times greater than today, causing the rain and ocean waters to be more acidic than today. We therefore conclude that CO2 alone (without a significant contribution from methane) could have provided the necessary greenhouse effect to maintain liquid oceans on the early Earth.

Greenhouse Effect↗
NASA NTRS2005

Comparative Planetary Mineralogy: Valence State Partitioning of Cr, Fe, Ti, and V Among Crystallographic Sites in Olivine, Pyroxene, and Spinel from Planetary Basalts

We have considered the valence-state partitioning of Cr, Fe, Ti, and V over crystallographic sites in olivine, pyroxene, and spinel from planetary basalts. The sites that accommodate these cations are the M2 site (6-8 coordinated) and M1 site (6 coordinated) in pyroxene, the M2 site (6-8 coordinated) and M1 site (6 coordinated) in olivine, and the tetrahedral and octahedral sites in spinel. The samples we studied are basalts from Earth, Moon, and Mars, which have fO2 conditions that range from IW-2 (Moon) to IW+6 (Earth) with Mars somewhere between at IW to IW+2. In this range of fO2 the significant elemental valences are (from low to high fO2) Ti4+, V3+, Fe2+, Cr2+, Cr3+, V3+, V4+, and Fe3+. V2+ and Ti3+ play a minor role in the phases considered for the Moon, and are probably in very low concentrations. V5+ plays a minor role in these phases in terrestrial basalts because it is probably in lower abundance than V4+ and it has an ionic radii that is so small (0.054 nm, 6- coordinated,[1]) that it is almost at the lower limit for octahedral coordination. The role of Cr2+ in the Moon is significant, as Sutton et al. [2] found that lunar olivine contains mostly Cr2+ while coexisting pyroxene contains mostly Cr3+. Hanson one vacancy only accommodates one V4+. Thus more vacancies are required in V4+ substitutions into olivine. In the Moon V3+ is much more abundant than V4+ [7, 8]. Thus in lunar chromite V3+ follows Cr3+, whereas in Earth V4+ (which is much greater in abundance than V3+) follows Ti4+ (eg in ulv spinel). We could go on in this vein for some time but space limitations do not permit us to do so.

Papike, J. J.↗
NASA NTRS2005

Weathering of Basaltic Rocks from the Gusev Plains up into the Columbia Hills from the Perspective of the MER Mossbauer Spectrometer

Rocks on the ejecta blanket of Bonneville crater and along Spirit s traverse over the Gusev plains towards the Columbia Hills are angular and strewn across the surface. They have a basaltic composition [1,2], and their Mossbauer spectra are dominated by an olivine doublet [1]. The ubiquitous presence of abundant olivine in rocks and in surrounding soil suggests that physical rather than chemical weathering processes currently dominate the plains at Gusev crater [1]. However, MB spectra of rocks and outcrops in the Columbia Hills suggest more aggressive alteration processes have occurred. Ascending into the hills, Spirit encountered outcrop and rocks exhibiting layered structures. Some scattered rocks at the foot of the Columbia Hills appeared "rotten" or highly altered by physical and/or chemical processes (fig. 1). Mossbauer spectra of those rocks show a decrease in olivine accompanied by an increase in the Fe-oxides magnetite, hematite, and nanophase Fe3+ -oxides (fig. 2), suggesting that chemical weathering processes in the presence of water have altered these rocks and outcrops.

Schroeder, C.↗
NASA NTRS2007

Biogeochemical Activity of Siderophilic Cyanobacteria: Implications for Paleobiogeochemistry

Understanding the patterns of iron oxidation by cyanobacteria (CB) has tremendous importance for paleobiogeochemistry, since cyanobacteria are presumed to have been involved in the global oxidation of ferrous iron during the Precambrian (Cloud, 1973). B.K. Pierson (1999, 2000) first proposed to study iron deposition in iron-depositing hot springs (ID HS) as a model for Precambrian Fe(2+) oxidation. However, neither the iron-dependent physiology of individual species of CB inhabiting iron-depositing hot springs nor their interactions with minerals enriched with iron have been examined thoroughly. Such study could shed light on ancient iron turnover. Cyanobacterial species isolated from ID HS demonstrate elevated tolerance to colloidal Fe(3+) (= 1 mM), while a concentration of 0.4 mM proved toxic for mesophilic Synechocystis PCC 6803. Isolates from ID HS require 0.4-0.6 mM Fe3+ for maximal growth while the iron requirement for Synechocystis is approximately one order of magnitude lower. We have also demonstrated that thick polysaccharide sheaths around cells of CB isolated from ID HS serve as repositories for precipitated iron. The growth of the mesophilic cyanobacteria Phromidium aa in iron-saturated (0.6 mM) DH medium did not lead to iron precipitation on its filament surfaces. However, a 14.3 fil.2 culture, isolated from an ID HS and incubated under the same conditions, was covered with dense layer of precipitated iron. Our results, taken together with Pierson s data concerning the ability of Fe2+ to stimulate photosynthesis in natural CB mats in ID HS, suggest that CB inhabiting ID HS may constitute a new group of the extremophiles - siderophilic CB. Our recent experiments have revealed for the first time that CB isolates from ID HS are also capable of biodeterioration - the etching of minerals, in particular glasses enriched with Fe, Al, Ti, O, and Si. Thus, Precambrian siderophilic cyanobacteria and their predecessors could have been involved not only in iron deposition but also in the global release of elements. The ability of siderophilic CB to participate in iron turnover make them appropriate candidates for biotechnological processes.

Brown, Igor I.↗
NASA NTRS2007

Iron Mineralogy and Aqueous Alteration on Mars from the MER Moessbauer Spectrometers

The twin Mars Exploration Rovers Spirit (Gusev crater) and Opportunity (Meridiani Planum) used MIMOS II Moessbauer spectrometers to analyze martian surface materials in the first application of extraterrestrial Moessbauer spectroscopy. The instruments acquired spectra that identified the speciation of Fe according to oxidation state, coordination state, and mineralogical composition and provided quantitative information about the distribution of Fe among oxidation states, coordination states, and Fe-bearing phases. A total of 12 unique Fe-bearing phases were identified: Fe(2+) in olivine, pyroxene, and ilmenite; Fe(2+) and Fe(3+) in magnetite and chromite; Fe(3+) in nanophase ferric oxide (npOx), hematite, goethite, jarosite, an unassigned Fe3+ sulfate, and an unassigned Fe(3+) phase associated with jarosite; and Fe(0) in kamacite. Weakly altered basalts at Gusev crater (SO3 = 2.5 +/- 1.4 wt.% and Fe(3+)/Fe(sub T) = 0.24 +/- 0.11) are widespread on the Gusev plains and occur in less abundance on West Spur and Husband Hill in the Columbia Hills. Altered low-S rocks (SO3 = 5.2 +/- 2.0 wt.% and Fe(3+)/Fe(sub T) = 0.63 +/- 0.18) are the most common type of rock in the Columbia Hills. Ilm-bearing, weakly altered basalts were detected only in the Columbia Hills, as was the only occurrence of chromite in an altered low-S rock named Assemblee. Altered high-S rocks (SO3 > 14.2 wt.% and Fe(3+)/Fe(sub T) = 0.83 +/- 0.05) are the outcrop rocks of the ubiquitous Burns formation at Meridiani Planum. Two Fe(0)-bearing rocks at Meridiani Planum (Barberton and Heat Shield Rock) are meteorites. Laguna Class soil is weakly altered (SO3 = 6 +/- 2 wt.% and Fe(3+)/Fe(sub T) = 0.29 +/- 0.08) and widely distributed at both Gusev crater and Meridiani Planum, implying efficient global mixing processes or a global distribution of precursor rocks with comparable Fe mineralogical compositions. Paso Robles Class soil is heavily altered (SO3 approx. 31 wt.% and Fe(3+)/Fe(sub T) = 0.83 +/- 0.05), is relatively uncommon, and occurs as subsurface deposits in the Columbia Hills. Berry Class soil is also heavily altered (SO3 = 5 +/- 1 wt.% and Fe(3+)/Fe(sub T) = 0.60 +/- 0.13) and occurs at Meridiani Planum as lag deposits, at the crests of aeolian bedforms, and as isolated pockets on outcrop surfaces. Magnetite is identified as the strongly magnetic component in martian soil. Jarosite (in the Burns outcrop at Meridiani Planum) and goethite (in Clovis Class rocks at Gusev crater) are mineralogical markers for aqueous processes because they contain the hydroxide anion (OH(-)) as an essential part of their structure. Each yields approx.10 wt.% H2O upon dehydroxylation. The presence of Fe sulfates on opposite sides of Mars is evidence that aqueous processes under acid sulfate conditions are or were common. Except for Independence Class rocks in the Columbia Hills, the overall Fe mineralogical compositions and similar basaltic bulk chemical compositions (calculated with respect to S = Cl = 0) of the population of altered rocks analyzed by MER imply isochemical alteration of basaltic precursors at low water-to-rock ratios.

Morris, Richard V.↗
NASA NTRS2011

Experimental Acid Weathering of Fe-Bearing Mars Analog Minerals and Rocks: Implications for Aqueous Origin of Hematite-Bearing Sediments in Meridiani Planum, Mars

A working hypothesis for Meridiani evaporite formation involves the evaporation of fluids derived from acid weathering of Martian basalts and subsequent diagenesis [1, 2]. However, there are no reported experimental studies for the formation of jarosite and gray hematite (spherules), which are characteristic of Meridiani rocks from Mars analog precursor minerals. A terrestrial analog for hematite spherule formation from basaltic rocks under acidic hydrothermal conditions has been reported [3], and we have previously shown that the hematite spherules and jarosite can be synthetically produced in the laboratory using Fe3+ -bearing sulfate brines under hydrothermal conditions [4]. Here we expand and extend these studies by reacting Mars analog minerals with sulfuric acid to form Meridiani-like rock-mineral compositions. The objective of this study is to provide environmental constraints on past aqueous weathering of basaltic materials on Mars.

Golden, D. C.↗
NASA NTRS2011

Moessbauer Spectroscopy of Martian and Sverrefjell Carbonates

Mars, in its putative "warmer, wetter: early history, could have had a CO2 atmosphere much denser than its current value of <10 mbar. The question of where all this early CO2 has gone has long been debated. Now, several instruments on Mars Exploration Rover (MER) Spirit, including its Moessbauer spectrometer MIMOS II, have identified Mg-Fe carbonate in rock outcrops at Comanche Spur in the Columbia Hills of Gusev Crater. With this finding, carbonate cements in volcanic breccia collected on Sverrefjell Volcano on Spitzbergen Island in the Svalbard Archipelago (Norway) during the AMASE project are mineralogical and possible process analogues of the newly discovered martian carbonate. We report further analyses of Mossbauer spectra from Comanche Spur and discuss their relationship to Mossbauer data acquired on Sverrefjell carbonates. The spectra were velocity calibrated with MERView and fit using MERFit. Instead of the "average temperature" Comanche spectrum (data from all temperature windows summed), we refit the Comanche data for QS within each temperature window, modeling as doublets for Fe2+(carbonate), Fe2+(olivine), and Fe3+(npOx). The temperature dependences of QS for the Comanche carbonate and for a low-Ca carbonate from Chocolate Pots in Yellowstone National Park (YNP) are shown; they are the same within error. For Comanche carbonate summed over 210-270 K, (CS, QS) = (1.23, 1.95) mm/s. The value of QS for Sverrefjell carbonate at 295 K, (CS, QS) = (1.25, 1.87) mm/s, is also plotted, and the plot shows that the QS for the Sverrefjell carbonate agrees within error with the Comanche data extrapolated to 295 K. This agreement is additional evidence that the Sverrefjell carbonates are Mossbauer analogues for the Comanche carbonates, and that both carbonates might have precipitated from solutions that became carbonate rich by passing through buried carbonate deposits.

Agresti, David G.↗
NASA NTRS2012

Chemical and Mineralogical Characterization of Acid-Sulfate Alteration of Basaltic Material on Mauna Kea Volcano, Hawaii: Jarosite and Hydrated Halloysite

Sulfates have been identified on the martian surface during robotic surface exploration and by orbital remote sensing. Measurements at Meridiani Planum (MP) by the Alpha-Particle X-ray Spectrometer (APXS) and Mossbauer (MB) instruments on the Mars Exploration Rover Opportunity document the presence of a ubiquitous sulfate-rich outcrop (20-40% SO3) that has jarosite as an anhydrous Fe3+-sulfate [1- 3]. The presence of jarosite implies a highly acidic (pH <3) formation environment [4]. Jarosite and other sulfate minerals, including kieserite, gypsum, and alunite have also been identified in several locations in orbital remote sensing data from the MEx OMEGA and MRO CRISM instruments [e.g. 5-8]. Acid sulfate weathering of basaltic materials is an obvious pathway for formation of sulfate-bearing phases on Mars [e.g. 4, 9, 10]. In order to constrain acid-sulfate pathways on Mars, we are studying the mineralogical and chemical manifestations of acid-sulfate alteration of basaltic compositions in terrestrial environments. We have previously shown that acidsulfate alteration of tephra under hydrothermal conditions on the Puu Poliahu cone (summit region of Mauna Kea volcano, Hawaii) resulted in jarosite and alunite as sulfate-bearing alteration products [11-14]. Other, more soluble, sulfates may have formed, but were leached away by rain and melting snow. Acidsulfate processes on Puu Poliahu also formed hematite spherules similar (except in size) to the hematite spherules observed at MP as an alteration product [14]. Phyllosilicates, usually smectite }minor kaolinite are also present as alteration products [13]. We discuss here an occurrence of acid-sulfate alteration on Mauna Kea Volcano (Hawaii). We report VNIR spectra (0.35-2.5 microns ASD spectrometer), Mossbauer spectra (MER-like ESPI backscatter spectrometer), powder XRD (PANalytical), and major element chemical compositions (XRF with LOI and Fe redox) for comparison to similar data acquired or to be acquired by MRO-CRISM and MEx OMEGA, MERMB, MSL-CheMin, and MER and MSL APXS, respectively.

Graff, Trevor G.↗
NASA NTRS2010

Metagenomic Study of Iron Homeostasis in Iron Depositing Hot Spring Cyanobacterial Community

Introduction: It is not clear how an iron-rich thermal hydrosphere could be hospitable to cyanobacteria, since reduced iron appears to stimulate oxidative stress in all domains of life and particularly in oxygenic phototrophs. Therefore, metagenomic study of cyanobacterial community in iron-depositing hot springs may help elucidate how oxygenic prokaryotes can withstand the extremely high concentrations of reactive oxygen species (ROS) produced by interaction between environmental Fe2+ and O2. Method: Anchor proteins from various species of cyanobacteria and some anoxygenic phototrophs were selected on the basis of their hypothetical role in Fe homeostasis and the suppression of oxidative stress and were BLASTed against the metagenomes of iron-depositing Chocolate Pots and freshwater Mushroom hot springs. Results: BLASTing proteins hypothesized to be involved in Fe homeostasis against the microbiomes from the two springs revealed that iron-depositing hot spring has a greater abundance of defensive proteins such as bacterioferritin comigratory protein (Bcp) and DNA-binding Ferritin like protein (Dps) than a fresh-water hot spring. One may speculate that the abundance of Bcp and Dps in an iron-depositing hot spring is connected to the need to suppress oxidative stress in bacteria inhabiting environments with high Fe2+ concnetration. In both springs, Bcp and Dps are concentrated within the cyanobacterial fractions of the microbial community (regardless of abundance). Fe3+ siderophore transport (from the transport system permease protein query) may be less essential to the microbial community of CP because of the high [Fe]. Conclusion: Further research is needed to confirm that these proteins are unique to photoautotrophs such as those living in iron-depositing hot spring.

Brown, I.↗
NASA NTRS2013

Water Contents of the Mantle Beneath the Rio Grande Rift: FTIR Analysis of Kilbourne Hole Peridotite Xenoliths

Although nominally anhydrous mantle minerals contain only trace amounts of water, they are the main reservoir of water in the mantle. Added up at the scale of the Earth's mantle, these trace amounts of water represent oceans worth in mass]. Mantle xenoliths from Kilbourne Hole in southern New Mexico are ideal to study mantle water distribution in a rift tectonic setting as they come from a recently‐erupted maar in the middle of the Rio Grande Rift. Eleven lherzolites, one harzburgite, and one dunite are being analyzed for water contents by FTIR. The xenoliths will also be analyzed for major and trace element composition, Fe3+/Summation (Fe) ratios, and characterized petrologically. Olivines exhibit variable water contents with less water at the rims compared to the cores. This is probably due to H loss during decompression and xenolith transport by the host magma. Mantle water contents appear to have been primarily preserved in the core of the olivines, based on diffusion modeling of the typically plateau-shaped water content profiles across these grains. Water concentrations are in equilibrium between clino- and orthopyroxene, but olivine concentrations are typically not in equilibrium with those of either pyroxene. Lherzolites analyzed so far have water contents of 2‐12 ppm H2O in olivines, 125‐165 ppm H2O in orthopyroxenes, and 328‐447 ppm H2O in clinopyroxenes. These water contents are similar to, but with a narrower range, than those for the respective minerals in other continental peridotite xenoliths. The lherzolites have bulk-rock (BR) Al2O3 contents that range between 3.17 and 3.78 wt%, indicating similar degrees of partial melting, which could explain the narrow range of their pyroxene water contents. Primitive mantle normalized rare earth element (REE) profiles of the bulk lherzolites vary from light REE depleted to flat, with no significant differences between, nor relation to, their mineral water contents. Consequently, the metasomatic agents that enriched LREEs in these lherzolites were most likely water-poor. The harzburgite and the dunite have lower weight percent Al2O3 compared to the lherzolites (2.11% and 0.34% respectively) indicating higher degrees of melting. Their olivine water contents, however, are similar to those of the lherzolites. Moreover, no correlations are observed between pyroxene water contents and indices of melting or metasomatism between the lherzolite group, the harzburgite, and the dunite, although the latter has the lowest pyroxene water contents. More samples will be analyzed to determine if the water contents are controlled by melting, metasomatism, or a combination of the two in the Kilbourne Hole mantle.

Schaffer, Lillian A.↗
NASA NTRS2014

Valence State Partitioning of V between Pyroxene and Melt for Martian Melt Compositions Y 980459 and QUE 94201: The Effect of Pyroxene Composition and Crystal Structure

A spiked (with REE, V, Sc) martian basalt Y980459 composition was used to synthesize olivine, spinel, and pyroxene at 1200 C at 5 oxygen fugacities: IW-1, IW, IW+1, IW+2, and QFM. The high spike levels for REE were used for two specific reasons. First, we wanted to be able to analyze REE by both electron microprobe and ion probe. Second, we wanted the most important "Others" components, (i.e., those outside the pyroxene quadrilateral such as Al, Cr3+, Fe3+, REE3+, V3+, V4+, etc.) to be REE3+Mg (Si,Al)2O6. At the doped levels we used, the most important "Others" component is REE3+ in the M2 site coupled with Al in the tetrahedral site. The goal of this paper is to explain the significant increase in the value of D(sub V)(sup pyroxene/melt) with increased Wo content of the pyroxene. We compare augite (Wo approx. 33), pigeonite (Wo approx. 13) and orthopyroxene (Wo approx 3.8). We also show olivine for comparison. The crystal chemical factors which account for this remarkable increase of DV with Wo are twofold. First, with Ca in the M2 site (as in diopside, CaMgSi2O6) the site is large and 8-coordinated while Mg in the M2 site (as in enstatite, Mg2Si2O6) the site is smaller and 6- coordinated. Second, tetrahedral Al in the pyroxene chains provides charge balance and makes the M2 site larger and more compliant for the introduction of REE.

Papike, J. J.↗
NASA NTRS2016

The Cr Redox Record of fO2 Variation in Angrites. Evidence for Redox Conditions of Angrite Petrogenesis and Parent Body

Angrites represent some of the earliest stages of planetesimal differentiation. Not surprisingly, there is no simple petrogenetic model for their origin. Petrogenesis has been linked to both magmatic and impact processes. Studies demonstrated that melting of chondritic material (e.g. CM, CV) at redox conditions where pure iron metal is unstable (e.g., IW+1 to IW+2) produced angrite-like melts. Alternatively, angrites were produced at more reducing conditions (<IW) with their exotic melt compositions resulting from carbonates in the source or from nebular condensation. Clearly, understanding what role fO2 plays in producing angrite magmas is critical for deciphering their petrogenesis and extending our understanding of primordial melting of asteroids. Calculations for the fO2 conditions of angrite crystallization are limited, and only preliminary attempts been made to understand the changes in fO2 that occurred during petrogenesis. Many of the angrites have phase assemblages which provide conflicting signals about redox conditions during crystallization (e.g., Fe metal and a Fe-Ti oxide with potential Fe3+. There have been several estimates of fO2 for angrites. Most notably, experiments examined the variation of DEu/DGd with fO2, between plagioclase and fassaitic pyroxene in equilibrium with an angrite melt composition. They used their observations to estimate the fO2 of crystallization to be approximately IW+0.6 for angrite LEW 86010. This estimate is only a "snapshot" of fO2 conditions during co-crystallization of plagioclase and pyroxene. Preliminary XANES analyses of V redox state in pyroxenes from D'Orbigny reported changes in fO2 from IW-0.7 during early pyroxene crystallization to IW+0.5 during latter episodes of pyroxene crystallization [15]. As this was a preliminary report, it presented limited information concerning the effects of pyroxene orientation and composition on the V valence measurements, and the effect of melt composition on valence and partitioning behavior of V. A closer examination of fO2 as recorded by Cr valence state in olivine will allow us to test models for primordial melting of chondritic material to produce the angrite parent melts. Here, we report the our initial stages of examining the origin and conditions of primordial melting on the angrite parent body and test some of the above models by integrating an experimental study of Cr and V valence partitioning between olivine [OL] and an angrite melt, with micro-scale determinations of Cr and V oxidation state in OL in selected "volcanic" angrites.

Shearer, Charles K.↗
NASA NTRS2016

Acid Sulfate Alteration on Mars

A variety of mineralogical and geochemical indicators for aqueous alteration on Mars have been identified by a combination of surface and orbital robotic missions, telescopic observations, characterization of Martian meteorites, and laboratory and terrestrial analog studies. Acid sulfate alteration has been identified at all three landing sites visited by NASA rover missions (Spirit, Opportunity, and Curiosity). Spirit landed in Gusev crater in 2004 and discovered Fe-sulfates and materials that have been extensively leached by acid sulfate solutions. Opportunity landing on the plains of Meridiani Planum also in 2004 where the rover encountered large abundances of jarosite and hematite in sedimentary rocks. Curiosity landed in Gale crater in 2012 and has characterized fluvial, deltaic, and lacustrine sediments. Jarosite and hematite were discovered in some of the lacustrine sediments. The high elemental abundance of sulfur in surface materials is obvious evidence that sulfate has played a major role in aqueous processes at all landing sites on Mars. The sulfate-rich outcrop at Meridiani Planum has an SO3 content of up to 25 wt.%. The interiors of rocks and outcrops on the Columbia Hills within Gusev crater have up to 8 wt.% SO3. Soils at both sites generally have between 5 to 14 wt.% SO3, and several soils in Gusev crater contain around 30 wt.% SO3. After normalization of major element compositions to a SO3-free basis, the bulk compositions of these materials are basaltic, with a few exceptions in Gusev crater and in lacustrine mudstones in Gale crater. These observations suggest that materials encountered by the rovers were derived from basaltic precursors by acid sulfate alteration under nearly isochemical conditions (i.e., minimal leaching). There are several cases, however, where acid sulfate alteration minerals (jarosite and hematite) formed in open hydrologic systems, e.g., in Gale crater lacustrine mudstones. Several hypotheses have been suggested for the aqueous formation of sulfate-bearing phases under acidic conditions on the surface of Mars including (1) sulfuric acid weathering of basaltic materials; (2) oxidative weathering of ultramafic igneous rocks containing sulfides; (3) acid fog weathering of basaltic materials, and (4) near-neutral pH subsurface solutions rich in Fe2(+) that were rapidly oxidized to Fe3(+), which produced excess acidity as iron was oxidized on exposure to O2 or photo-oxidized by ultraviolet radiation at the martian surface. Next, we briefly describe evidence for these hypothesis.

Ming, D. W.↗
NASA NTRS2016

Authigenesis/Diagenesis of the Murray Formation Mudstone in Gale Crater, Mars

The Mars Science Laboratory rover Curiosity has been exploring sedimentary deposits in Gale crater since August, 2012. The rover has traversed up section through approximately 150 m of sedimentary rocks deposited in fluvial, deltaic, and lacustrine environments (Bradbury group and overlying Mount Sharp group). The Murray formation lies at the base of the Mt. Sharp group and has been interpreted to be a finely laminated mudstone likely deposited in a subaqueous lacustrine environment. Four drill samples from several elevations in the Murray fm have been acquired by the rover's sampling system and delivered to the CheMin XRD instrument. The lower section of the Murray fm contains 2:1 phyllosilicate(s), hematite, jarosite, XRD amorphous materials, and primary basaltic minerals. Further up section, the Murray fm contains magnetite, cristobalite, tridymite, abundant Si-rich XRD amorphous materials along with plagioclase and K-feldspars. Murray formation materials appear to have been altered under an open hydrologic system based on the bulk chemistry of these materials measured by the Alpha Particle X-ray Spectrometer (APXS). The 2:1 phyllosilicate only occurs in the lowermost section of the Murray fm and may be detrital or formed during authigenesis of Murray fm materials, similar to the Fe-saponite and magnetite detected in a mudstone in the Yellowknife Bay fm near Curiosity's landing site (stratigraphically at the base of the Bradbury group). The occurrence of jarosite and hematite in the lower section indicates an acidic diagenetic event. These phases may have formed via several acidic alteration mechanisms, including (1) oxidative weathering of mafic igneous rocks containing sulfides; (2) sulfuric acid weathering of Fe-bearing phases; and (3) near-neutral pH subsurface solutions rich in Fe2(+) that were rapidly oxidized to Fe3(+), which produced excess acidity. The transition from abundant hematite in the lowermost Murray fm to magnetite moving up section may indicate changes in lake chemistry, i.e., variable redox conditions, possibly during authigenesis or subsequent diagenetic events. Tridymite, a high temperature mineral, (and possibly cristobalite) is detrital, potentially deposited in a lake from a distal silicic volcanic rock source or from crustal materials present prior to the Gale Crater impact event. Abundant Si-rich XRD amorphous materials in the upper sections of the Murray fm may be detrital or an aqueous alteration product of primary igneous phases and phyllosilicates. Curiosity's science team is still deciphering the authigenesis and diagenetic events that formed the Murray fm. The mineralogy and geochemistry of the formation suggest a complicated history with several (many?) episodes of aqueous alteration under a variety of environmental conditions.

Ming, D. W.↗
NASA NTRS2016

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approx.576-867 C. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Metallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120deg triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3+, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

Srinivasan, P.↗