We explore the use of femtosecond laser pulses to clean a variety of colors of spray paint from the Moruya granite, a stone with high heritage value that is widely used for monuments and sculptures in Sydney and New South Wales (Australia). The efficiency of the cleaning treatment and the effects on the stone substrate are evaluated using optical microscopy, optical profilometry, Raman spectroscopy, energy-dispersive X-ray spectroscopy, and colorimetry. We demonstrate that femtosecond laser cleans granite without damaging it and without discoloration when the laser fluence is set below the damage threshold of the stone.

In Gale crater on Mars, the rover Curiosity has discovered evidence of fluid mobilization of the redox‐sensitive element manganese. We present results for Mn from Curiosity's Alpha Particle X‐ray Spectrometer (APXS), which show that the average MnO concentration in mudstone‐dominated sedimentary units (0.22 wt%) is about one‐half of the concentration in the average Mars crust (0.44 wt%). Geochemical trends indicate that Mn in the sedimentary bedrock, most of which has a basaltic provenance, was leached by chemical alteration and dissolution. In >350 vertical meters of mudstone‐dominated strata, the apparent leaching of Mn and retention of Fe in Fe‐O‐H phase(s) resulted in the fractionation of Fe and Mn, indicating relatively moderate Eh‐pH fluid conditions that were not highly alkaline, reducing, or oxidizing. Exceptions are fracture‐associated, silica‐rich haloes where both Mn and Fe were leached by low pH fluids. The rover also discovered Mn‐rich veins, nodules, and patchy, dark coatings on rock surfaces, which are variably associated with enrichments in Fe, P, Cl, and/or Zn. These Mn‐rich features represent ∼1% of the 1029 APXS measurements acquired over ∼25 km of rover traverse. A thermochemical model shows that dissolved Mn2+ could have been concentrated via evaporation, sublimation, and/or freezing. Manganese was then likely precipitated in localized features when >99.99% of the Mn2+‐bearing water was removed from the system. These findings indicate that Mn was mobile in Gale crater and therefore bioavailable as a potential energy source for life.

The surface of Mercury is enriched in sulfur, with up to 4 wt.% detected by the NASA MESSENGER mission, and has been challenging to understand in the context of other terrestrial planets. We posit, that magmatic S was mobilized as a gas phase in volcanic and impact processes near the surface, exposing silicates to a hot S-rich gas at reducing conditions and allowing conditions for rapid gas-solid reactions. Here, we present novel experiments on the reaction of Mercury composition glasses with reduced S-rich gas, forming Ca-and Mg-sulfides. The reaction products provide porous and fragile materials that create previously enigmatic hollows on Mercury. Our model predicts that the gas-solid reaction forms Ca-Mg Fe-Ti-sulfide assemblages with SiO2 and aluminosilicates, distinct from formation as magmatic minerals. The ESA/JAXA BepiColombo mission to Mercury will allow this hypothesis to be tested.(c) 2022 Elsevier B.V. All rights reserved.

FROM THE GROKEN DRILL SITE. J.A. Berger1*, S.J.V. VanBommel2, B.C. Clark3, R. Gellert4, C.H. House5, P.L. King6, M.A. McCraig4, D.W. Ming1, C.D. O’Connell-Cooper7, M.E. Schmidt8, L.M. Thompson7, A.S. Yen9. 1NASA Johnson Space Center, Houston, USA; 2Washington University in St. Louis, St. Louis, USA; 3Space Science Institute, Boulder, USA; 4University of Guelph, Guelph, CAN; 5Penn State, University Park, USA; 6Australian National University, Canberra, AUS; 7University of New Brunswick, Fredericton, CAN; 8Brock University, St. Catharines, CAN; 9JPL-Caltech, Pasadena, USA; *jeffrey.a.berger@nasa.gov.

Salt-rich deposits may be more widespread on planetary surfaces than is generally appreciated. Remote observations, laboratory studies of meteorites, and cosmochemical constraints all point towards widespread occurrences of salts (including halides, sulfates, and (bi)carbonates) on asteroids, icy bodies, Mars, and elsewhere. We have investigated the mid-infrared (1.8-25 mu m) reflectance spectral properties of mixtures of chondritic (ordinary, enstatite and carbonaceous) meteorites with potassium bromide; a mid-infrared transmissive salt like all halides. Our results demonstrate that halide-chondrite mixtures provide spectral signatures that either reveal the presence of transmissive materials or provide evidence for highly porous regolith. Previously, the nature of the surfaces of the asteroids 624 Hektor and 21 Lutetia was inferred using a limited range of spectra from halide-chondrite mixtures. Here, we provide an extensive dataset of halide-chondrite mixtures to encompass a wider set of possible surface compositions.

Sulphur dioxide (SO 2 ) is removed from flue gases prior to discharge into the atmosphere by high temperature sulphation reactions with the mineral calcite (CaCO 3 ) in the form of calcite aggregates such as limestone. The efficiency of this industrial-scale process is constrained by the self-inhibiting growth of anhydrite (CaSO 4 ) along calcite grain boundaries. Using very high resolution X-ray μCT and Scanning Electron Microscopy we show, for the first time, how the sulphation reaction is initiated by the anisotropic thermal expansion of calcite grains to produce high inter-grain permeability. In turn fast gas-solid reaction occurs to produce a network of porous anhydrite layers between grains. Individual calcite grains are then free to rotate and translate with respect to each other as the sulphation reaction proceeds. Grain translations of up to 24 μm and rotations of up to 0.64 degrees have been tracked in samples of a highly compacted calcite aggregate (Carrara Marble) across up to 600,000 grains through heating and cooling cycles during exposure to SO 2 gas flow at temperatures from 600 to 750 °C at one atmosphere. Such grain kinematics help to maintain gas phase permeability in the solid reactant and mitigate the inhibitory growth of porous anhydrite on grain boundaries.

Sulfur dioxide (SO2(g)) is an important gas species in most common volcanic settings on 8 Earth including subduction zones (Shinohara 2013). The relative abundances of SO2(g) may vary at 9 a volcano over time with the highest rates of SO2(g) emissions occurring during eruptive degassing 10 and lesser amounts emitted continuously during quiescent degassing, resulting in a large total 11 amount of SO2(g) integrated over time of the order of 10 Mt/a (McCormick et al. 2013; Shinohara 12 2013; Henley and Hughes 2016). Much of the emitted SO2(g) is released at high temperatures. For 13 instance, gas mixtures sampled at the highest temperature volcanic vents reach 1131 °C at Erta Ale 14 volcano and these are the most likely to be representative of the volcanic gas phase (de Moor et al. 15 2013). 16

Introduction: Phosphorus mobility on the martian surface is fundamental to habitability because the element is essential for biochemical reactions and biological structures. The Spirit, Opportunity, and Curiosity rovers have discovered a range of P concentrations on the martian surface suggesting pervasive mobility of the element [e.g., 1, 2, 3]. A key pathway for P mobilization is via dissolution of primary phosphates (apatite, merrillite) [4, 5] and reprecipitation of P-rich phases in soils, veins, alteration haloes, localized features and/or rock matrix. The secondary P-bearing phases are not fully characterized by rover observations; where primary apatite is not apparent, P is variably associated with Ca, Fe, Al, and Mn with no detectable affinity with any single cation [e.g., 1, 2, 3]. In Mars analogue samples from the summit of Maunakea, Hawai’i, we have identified an association of P with S in secondary aluminum-phosphate-sulfate (APS) minerals. Here, we describe the occurrence of APS minerals in analogue samples and propose a similar fate for P in S-rich martian systems. Samples and Methods: Two Maunakea summit samples representative of acid-sulfate alteration processes were investigated: (1) a tephra fragment with an unaltered interior and an ~1-cm-thick alteration rind (HWMK953) and (2) breccia containing highly altered lithic fragments cemented by sulfates, phyllosilicates, and amorphous silica-rich material (HWMK959). The average unaltered parent composition of the summit tephra is hawaiite. A field-emission SEM was used to acquire an EDS element map of the breccia and spot EDS analyses on polished thin sections of both samples. Bulk chemistry and mineralogy of the breccia sample was obtained with powder X-ray diffraction (XRD) and X-ray fluorescence (XRF). Results: Unaltered tephra: The least-altered zone of the tephra (HWMK953) is typical for unaltered hawaiitic/mugeartitic volcanics capping Maunakea, which have bulk P2O5 ~1 wt% [6, 7]. Phosphorus is contained within apatite, which occurs as 1-100 μm hexagonal and acicular grains (mostly skeletal) in the glass matrix and as inclusions in olivine. F, Cl, and OH were not analyzed with EDS and S was below detection limits. Altered lithic material: The altered rock fabric largely maintains its primary trachytic texture, albeit with silica pseudomorphs after feldspar, pyroxene, and olivine, and Ti-oxide pseudomorphs after Fe-Ti-oxide. No residual primary apatite grains were found. Figure 1: Element maps of P, S, and Si in acid-sulfate altered breccia (HWMK959). Si indicates altered lithic fragments (green) cemented together by Pand S-rich secondary materials (magenta and light violet).

Sulfur dioxide [SO2(g)] is the most abundant sulfur-bearing volcanic gas species on Earth. From its magmatic origin at depth to expulsion at the surface via either persistent degassing or large explosive volcanic eruptions, SO2(g) interacts with silicate materials at elevated temperatures. Similar high-temperature reactions also occur in the volcanic systems and the atmospheres of Venus, the Galilean moon Io, and in Mars’ past, as well in industrial flue-gas processing. We present an experimental investigation of the reaction between SO2(g), glasses and supercooled melts in the system anorthite–diopside–albite (CaAl2Si2O8–CaMgSi2O6–NaAlSi3O8). The samples were exposed to SO2(g) at 600–800 °C for experimental durations of 10 min to 24 h. The reactions resulted in the formation of sulfate coatings and modified the near-surface composition of the silicate samples. The predominant sulfate reaction product is CaSO4, with hydrated MgSO4 or Na2SO4 also observed in some experiments. In the anorthite–diopside system, the reaction extent strongly depends on the temperature relative to the glass transition temperature (Tg). Above Tg, in reactions with supercooled melts, the reaction forms up to 20 times more sulfate. The overall rate of sulfate formation is controlled by the diffusive flux of Ca, Mg and Na from the increasingly depleted silicate to the surface where the reaction with SO2(g) occurs. The sulfate-forming reaction results in a volume increase relative to the unreacted silicate. When this reaction occurs in the subvolcanic environment it causes an increased molar volume that may close veins, reducing the permeability and decrease the SO2(g) flux at the surface. An increase in the SO2(g) flux would then result in the opening of new veins, which may be accompanied by seismic activity. Additionally, the change in molar volume may itself trigger seismicity. The strong preferential uptake of Ca into the sulfate reaction product results in a Si- and Al-enriched silicate. In the sulfate, the Ca component may be mobilized by secondary processes such as through the interaction with meteoric fluids. We recommend that the products of such gas–solid reactions should be the object of remote and robotic investigations of planetary environments with volcanic histories such as on Mars, Io, Venus and Mercury.

Martian magmas were likely enriched in S and Cl with respect to H 2 O. Exsolution of a vapor phase from these magmas and ascent of the gas bubbles through the magma plumbing system would have given rise to shallow magmas that were gas‐charged. Release and cooling of this gas from lava flows during eruption may have resulted in the addition of a significant amount of vapor‐deposited phases to the fines of the surface. Experiments were conducted to simulate degassing of gas‐charged lava flows and shallow intrusions in order to determine the nature of vapor‐deposited phases that may form through this process. The results indicate that magmatic gas may have contributed a large amount of Fe, S, and Cl to the Martian surface through the deposition of iron oxides (magnetite, maghemite, and hematite), chlorides (molysite, halite, and sylvite), sulfur, and sulfides (pyrrhotite and pyrite). Primary magmatic vapor‐deposited minerals may react during cooling to form a variety of secondary products, including iron oxychloride (FeOCl), akaganéite (Fe 3+ O (OH,Cl)), and jarosite (KFe 3+ 3 (OH) 6 (SO 4 ) 2 ). Vapor‐deposition does not transport significant amounts of Ca, Al, or Mg from the magma and hence, this process does not directly deposit Ca‐ or Mg‐sulfates.

GAS/MINERAL SURFACE REACTION ON MARS N.J. DiFrancesco, Rogers, A.D, M. Yant, H. Nekvasil and P.L. King. SUNY Oswego Department of Atmospheric and Geological Sciences, Oswego, NY 13126 Nicholas.difrancesco@oswego.edu, Stony Brook University Department of Geosciences, Stony Brook, NY 11794, Deanne.Rogers@stonybrook.edu Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD 21218, marcella.yant@jhu.edu, Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia, penny.king@anu.edu.au.

interior of silica glass tube after degassing and cooling, and EDS spectrum suggesting FeOCl. Fig. 1. Octahedra of maghemite adhered to the wall of the silica glass tube by Na-K-Fe chlorides (dark crystals in a. and b.) MARTIAN DUST: WHAT ROLE COULD MAGMATIC GAS HAVE PLAYED IN ITS CHEMICAL SIGNATURE? H. Nekvasil1, N. J. DiFrancesco2, A. D. Rogers1 and P. L. King3, 1Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, Hanna.Nekvasil@stonybrook.edu, 2SUNY Oswego, Department of Atmospheric and Geological Sciences, Oswego, NY 13126, Nicholas. DiFrancesco@oswego.edu, 3Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia, penny.king@anu.edu.au.

hered to the wall of the silica glass tube by Na-K-Fe chlorides (dark crystals in a. and b.) MARTIAN DUST: CONTRIBUTIONS OF CONDENSATES FROM MAGMATIC GAS. H. Nekvasil1, N. J. DiFrancesco2, A. D. Rogers1 and P. L. King3, 1Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, Hanna.Nekvasil@stonybrook.edu, 2SUNY Oswego, Department of Atmospheric and Geological Sciences, Oswego, NY 13126, Nicholas. DiFrancesco@oswego.edu, 3Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia, penny.king@anu.edu.au.

The transport of metals in volcanic gases on the Moon differs greatly from their transport on the Earth because metal speciation depends largely on gas composition, temperature, pressure and oxidation state. We present a new thermochemical model for the major and trace element composition of lunar volcanic gas during pyroclastic eruptions of picritic magmas calculated at 200–1500°C and over 10−9–103bar. Using published volatile component concentrations in picritic lunar glasses, we have calculated the speciation of major elements (H, O, C, Cl, S and F) in the coexisting volcanic gas as the eruption proceeds. The most abundant gases are CO, H2, H2S, COS and S2, with a transition from predominantly triatomic gases to diatomic gases with increasing temperatures and decreasing pressures. Hydrogen occurs as H2, H2S, H2S2, HCl, and HF, with H2 making up 0.5–0.8mol fractions of the total H. Water (H2O) concentrations are at trace levels, which implies that H-species other than H2O need to be considered in lunar melts and estimates of the bulk lunar composition. The Cl and S contents of the gas control metal chloride gas species, and sulfide gas and precipitated solid species. We calculate the speciation of trace metals (Zn, Ga, Cu, Pb, Ni, Fe) in the gas phase, and also the pressure and temperature conditions at which solids form from the gas. During initial stages of the eruption, elemental gases are the dominant metal species. As the gas loses heat, chloride and sulfide species become more abundant. Our chemical speciation model is applied to a lunar pyroclastic eruption model with isentropic gas decompression. The relative abundances of the deposited metal-bearing solids with distance from the vent are predicted for slow cooling rates (<5°C/s). Close to a volcanic vent we predict native metals are deposited, whereas metal sulfides dominate with increasing distance from the vent. Finally, the lunar gas speciation model is compared with the speciation of a H2O-, CO2- and Cl-rich volcanic gas from Erta Ale volcano (Ethiopia) as an analogy for more oxidized planetary eruptions. In the terrestrial Cl-rich gas the metals are predominantly transported as chlorides, as opposed to metallic vapors and sulfides in the lunar gas. Due to the presence of Cl-species, metal transport is more efficient in the volcanic gas from Erta Ale compared to the Moon.

Introduction: Sulfur, F, Cl and a range of metals (Zn, Ga, Cu, Pb, Ni and other elements) are found coating glass beads in basaltic pyroclastic deposits from Apollo 17 (orange glass) and Apollo 15 (green glass) [1, 2]. The coatings are believed to have deposited from a volcanic gas during decompression and cooling of the eruptive plume [1, 3]. Using volatile element (H, C, Cl, S, F) concentrations measured in Apollo 17 orange glass beads [4, 5] and assuming an oxygen fugacity two log units below the iron-wüstite buffer (IW-2), we have derived a model for the composition of a lunar volcanic gas (mole%: H=31.8, O=15.4, C=15.9, Cl=0.2, S=34.6, F=2). Adding 0.001 mole% (arbitrarily set far below saturation) of the metals Zn, Ni, Pb, Ga, Cu and Fe, we have calculated the speciation of the bulk composition at pressures from 10 to 10 bar and from 500 to 1500 °C using a Gibbs Free energy minimization approach. Here we present a new model linking the thermochemical evolution of the lunar volcanic gas and the deposition of metal species during isentropic decompression and cooling with a simple ballistic flight path of the lunar glass beads onto which the metal species deposit. Isentropic decompression and cooling: The decompression and cooling of volcanic gas mixtures in eruption plumes is reasonably modeled as adiabatic [6, 7, 8] following isenthalpic or isentropic paths (Fig. 1). We use the isentropic path for our model, because lunar fire fountain eruptions decompress into the near vacuum and frictional heat loss is likely negligible. The eruption temperature at the vent is set to 1450 °C which is just above the liquidus temperatures of orange and green glasses [1298 to 1448 °C; 9]. The pressure at the vent, 0.1 bar is chosen in analogy to observations of explosive volcanic eruptions on Jupiter’s moon Io [10, 11, 12, 13]. The pressure-temperature conditions at which equal amounts of metals are in the gas phase and in the solid phase (∑M(g) / ∑M(S) = 1) are shown in Fig. 1. For the more refractory metals such as Cu, Fe and Ni this condition requires high temperatures (> 900 °C) and pressures near the vacuum. Pb, Zn and Ga can exist in the vapor phase at very low pressures (< 10 bar), even at temperatures below 700 °C. Despite its lower vapor pressure, Pb is more abundant in the gas phase at higher pressures and lower temperatures than Zn, because it forms relatively more stable sulfide and chloride species in the gas phase over most of the pressure and temperature range, increasing its volatility relative to Zn which occurs mainly as Zn(g). Fig. 1. The contours show the pressure and temperature conditions at which equal mole fractions of the metal are in the gas and solid phases. The stippled red line is the path of isenthalpic expansion and the solid red line is the isentropic expansion path of an ideal diatomic gas such as CO.