ALBERT

Description: Palagonitization is a common, but imperfectly defined process that greatly modifies the physical and chemical properties of glassy basaltic tephra deposited in subaquatic/subglacial environments on Earth and perhaps Mars. It also results in textures and mineralogies that are distinct from other forms of (mainly pedogenic) low temperature alteration. Specifically, the process of palagonitization (1) initially results in the formation of palagonitized glass', a quasi- or nano-crystalline, rind-like material that contains smectite, as well as lesser amounts of other clays (e.g. serpentine), and (2) eventually results in consolidation of tephra, mediated through the accretion of palagonitized glass and later-formed authigenic cements. Conversely, pedogenic weathering of glassy basaltic tephra is characterized by disaggregation of tephra, and formation of a wide range of pedogenic products, including layer silicates (although not primarily smectite), short-range-order aluminosilicates and oxyhydroxides, whose composition reflects the intensity of the weathering environment. These mineralogical and textural properties can be readily recognized through a variety of techniques including electron microscopy/microprobe analysis, reflectance spectroscopy, X-ray diffraction and soil chemistry. Analyses of samples collected from the summit regions of Kilauea and Mauna Kea volcanoes on the island of Hawaii are presented here in order to illustrate differences between palagonitization and pedogenic weathering of glassy basaltic tephra. In the young Hawaiian tephras studied, palagonitization has occurred in response to hydrothermal activity shortly after deposition. Although some, non-hydrothermally affected tephras may eventually become palagonitized, those that have been strongly desilicated by intense pedogenic weathering will probably never become palagonitized.

Description: Ferrihydrite samples were collected from a thermal spring and a cold stream in the Landmannalaugar region of Iceland. Chemical and spectroscopic analyses have been performed on the air-dried and fine-grained fractions of these samples. The ferrihydrite from the cold stream is a pure sample, containing small amounts of Ca, P and Si. The ferrihydrite from the thermal spring is a less pure sample, containing larger amounts of amorphous Si and P with some of the Si incorporated in the ferrihydrite structure. The spectral character of these Icelandic ferrihydrites is compared with those of synthetic ferrihydrites and other iron oxide/oxyhydroxide minerals. Ferrihydrite is characterized by a broad Fe3+ excitation band near 10 900 cm-1 (c. 0.92 {micro}m), a strong Fe-O vibrational feature near 475 cm-1 (c. 21 {micro}m), and multiple bands due to H2O and OH. Highly pure ferrihydrite has a pair of spectral bands near 1400 and 1500 cm-1 (c. 7 {micro}m). Natural ferrihydrites frequently exhibit an extra band near 950-1050 cm-1 (c. 10 {micro}m) that is attributed to Si-O bonds. Hydrothermal springs may have been present at one time on Mars in association with volcanic activity. Ferrihydrite formation in such an environment may have contributed to the ferric oxide-rich surface material on Mars.

Description: With the arrival of Curiosity on Mars, the MSL has started its ground validation of some of the phyllosilicate characterization carried out with remote sensing near-IR spectroscopy from orbital instruments. However, given the limited range of action of the rover, phyllosilicate identification and characterization will have to rely mainly on orbital near-IR data. Investigation of Earth analogs can greatly assist interpretation of martian spectra and enable more robust analyses. In this contribution, Mg/Fe-rich clays from submarine hydrothermal origin that had been thoroughly characterized previously were investigated with near-IR reflectance spectroscopy. The clays are mixed-layer glauconite-nontronite, talc-nontronite, talc-saponite, and nontronite samples. The hydroxyl bands in the range 2.1–2.35 μm were decomposed into their several individual components to investigate correlations between the octahedral chemistry of the samples and the normalized intensity of several bands. Good correlations were found for the samples of exclusive dioctahedral character (glauconite-nontronite and nontronite), whereas poor or no correlations emerged for the samples with one (talc-nontronite) or two (talc-saponite) trioctahedral layer components, indicating a more complex spectral response. Because these bands analyzed are a combination of the fundamental OH stretching and OH bending vibrations, the response of these fundamental bands to octahedral chemistry was considered. For 2:1 dioctahedral phyllosilicates, Fe and Mg substitution for Al displaces both fundamental bands to lower wavenumbers (longer wavelengths), so that their effect on the position of the combination band is coherent. In contrast, for trioctahedral clays, Al and Fe 3+ substitution of octahedral Mg displaces the OH stretching band to lower wavenumber values, and the OH bending band to higher wavenumber values, resulting in partial or total mutual cancelation of their effects. As a result, clays with near-IR spectra indicating Mg-dominated octahedral compositions may in fact contain abundant Fe and some Al substitution. Thus, remote-sensing near-IR mineralogical and chemical identification of clays on Mars appears relatively straightforward for dioctahedral clay minerals but more problematic for trioctahedral clays, for which it may require a more detailed investigation of their near-IR spectra.

Description: The ferric oxyhydroxide minerals akaganéite and schwertmannite are associated with acidic environments and iron alteration on Earth and may be present on Mars as well. These minerals have a tunnel structure and are crystallographically related. The extended visible region reflectance spectra of these minerals are characterized by a broad Fe 3+ electronic transition centered near 0.92 μm, a reflectance maximum near 0.73 μm, and a shoulder near 0.59 μm. The near-infrared (NIR) reflectance spectra of each of these minerals are dominated by broad overtones and combinations of the H 2 O vibration features. These occur near 1.44–1.48 and 1.98–2.07 μm (~6750–6950 and 4830–5210 cm –1 ) in akaganéite spectra, while in schwertmannite spectra they occur at 1.44–1.48 and 1.95–2.00 μm (~6750–6950 and 5005–5190 cm –1 ). Additional bands due to OH vibrational overtones are found near 1.42 μm (~7040 cm –1 ) in akaganéite and schwertmannite spectra and due to OH combination bands in akaganéite spectra at 2.46 μm (4070 cm –1 ) with weaker components at 2.23–2.42 μm (4134–4492 cm –1 ). A strong and broad band is observed near 2.8–3.1 μm (~3300–3600 cm –1 ) in reflectance and transmittance spectra of akaganéite and schwertmannite due to overlapping OH and H 2 O stretching vibrations. H 2 O bending vibrations occur near 1620 cm –1 (~6.17 μm) in akaganéite spectra and near 1630 cm –1 (~6.13 μm) in schwertmannite spectra with additional bands at lower frequencies due to constrained H 2 O molecules. OH bending vibrations occur near 650 and 850 cm –1 (~15.4 and 11.8 μm) in akaganéite spectra and near 700 cm –1 (~14.3 μm) in schwertmannite spectra. Sulfate vibrations are observed for schwertmannite as a 3 triplet at 1118, 1057, and 1038 cm –1 (~8.9, 9.5, and 9.6 μm), 1 at 982 cm –1 (~10.2 μm), 4 near 690 cm –1 (~14.5 μm), and 2 at 608 cm –1 (~16.5 μm). Fe-O bonds occur near 410–470 cm –1 (μm) for akaganéite and schwertmannite. Both minerals readily absorb H 2 O molecules from the environment and adsorb them onto the mineral surfaces and incorporate them into the tunnels. If akaganéite and schwertmannite were present on the surface of Mars they could enable transport of H 2 O from the near-surface to the atmosphere as the partial pressure of H 2 O varies diurnally.

Description: We have characterized complex iron- and sulfate-bearing samples from Rio Tinto (Spain) using X-ray diffraction (XRD), visible-near infrared reflectance (VNIR) spectroscopy, and laser Raman spectroscopy (LRS). Samples were collected for this study from the Peña de Hierro region of Rio Tinto because this site represents a natural acidic environment that is a potential analog for such environments on Mars. We report an evaluation of the capabilities of these three techniques in performing detailed mineralogical characterization of potential Mars-like samples from a natural acidic terrestrial environment. Sulfate minerals found in these samples include gypsum, jarosite, and copiapite, and iron hydroxide bearing minerals found include goethite and ferrihydrite. These sulfate and iron hydroxide/oxyhydroxide minerals were detected by XRD, VNIR, and LRS. Minor quartz was identified in some samples by XRD as well, but was not identified using VNIR spectroscopy. Coordinating the results from these three techniques provides a complete picture of the mineralogical composition of the samples. Field instruments were used for this study to mimic the kinds of analyses that could be performed in the field or on martian rovers.

Description: Sulfate minerals are important indicators for aqueous geochemical environments. The geology and mineralogy of Mars have been studied through the use of various remote-sensing techniques, including thermal (mid-infrared) emission and visible/near-infrared reflectance spectroscopies. Spectral analyses of spacecraft data (from orbital and landed missions) using these techniques have indicated the presence of sulfate minerals on Mars, including Fe-rich sulfates on the iron-rich planet. Each individual Fe-sulfate mineral can be used to constrain bulk chemistry and lends more information about the specific formational environment [e.g., Fe 2+ sulfates are typically more water soluble than Fe 3+ sulfates and their presence would imply a water-limited (and lower Eh) environment; Fe 3+ sulfates form over a range of hydration levels and indicate further oxidation (biological or abiological) and increased acidification]. To enable better interpretation of past and future terrestrial or planetary data sets, with respect to the Fe-sulfates, we present a comprehensive collection of mid-infrared thermal emission (2000 to 220 cm –1 ; 5–45 μm) and visible/near-infrared (0.35–5 μm) spectra of 21 different ferrous- and ferric-iron sulfate minerals. Mid-infrared vibrational modes (for SO 4 , OH, H 2 O) are assigned to each thermal emissivity spectrum, and the electronic excitation and transfer bands and vibrational OH, H 2 O, and SO 4 overtone and combination bands are assigned to the visible/near-infrared reflectance spectra. Presentation and characterization of these Fe-sulfate thermal emission and visible/near-infrared reflectance spectra will enable the specific chemical environments to be determined when individual Fe-sulfate minerals are identified.

Description: This study of the spectral properties of Ca-sulfates was initiated to support remote detection of these minerals on Mars. Gypsum, bassanite, and anhydrite are the currently known forms of Ca-sulfates. They are typically found in sedimentary evaporites on Earth, but can also form via reaction of acidic fluids associated with volcanic activity. Reflectance, emission, transmittance, and Raman spectra are discussed here for various sample forms. Gypsum and bassanite spectra exhibit characteristic and distinct triplet bands near 1.4–1.5 μm, a strong band near 1.93–1.94 μm, and multiple features near 2.1–2.3 μm attributed to H 2 O. Anhydrite, bassanite, and gypsum all have SO 4 combination and overtone features from 4.2–5 μm that are present in reflectance spectra. The mid-IR region spectra exhibit strong SO 4 3 and 4 vibrational bands near 1150–1200 and 600–680 cm –1 (~8.5 and 16 μm), respectively. Additional weaker features are observed near 1005–1015 cm –1 (~10 μm) for 1 and near 470–510 cm –1 (~20 μm) for 2 . The mid-IR H 2 O bending vibration occurs near 1623–1630 cm –1 (~6.2 μm). The visible/near-infrared region spectra are brighter for the finer-grained samples. In reflectance and emission spectra of the mid-IR region the 4 bands begin to invert for the finer-grained samples, and the 1 vibration occurs as a band instead of a peak and has the strongest intensity for the finer-grained samples. The 2 vibration is a sharp band for anhydrite and a broad peak for gypsum. The band center of the 1 vibration follows a trend of decreasing frequency (increasing wavelength) with increasing hydration of the sample in the transmittance, Raman, and reflectance spectra. Anhydrite forms at elevated temperatures compared to gypsum, and at lower temperature, salt concentration, and pH than bassanite. The relative humidity controls whether bassanite or gypsum is stable. Thus, distinguishing among gypsum, bassanite, and anhydrite via remote sensing can provide constraints on the geochemical environment.

Description: K + , Na + , Ca 2+ , Mg 2+ , Fe 2+ , Fe 3+ , and Al 3+ perchlorate salts were studied to provide spectral and thermal data for detecting and characterizing their possible presence on Mars. Spectral and thermal analyses are coordinated with structural analyses to understand how different cations and different hydration levels affect the mineral system. Near-infrared (NIR) spectral features for perchlorates are dominated by H 2 O bands that occur at 0.978–1.01, 1.17–1.19, 1.42–1.48, 1.93–1.99, and 2.40–2.45 μm. Mid-IR spectral features are observed for vibrations of the tetrahedral ClO 4 – ion and occur as reflectance peaks at 1105–1130 cm –1 (~8.6–9 μm), 760–825 cm –1 (~12–13 μm), 630 cm –1 (~15.9 μm), 460–495 (~20–22 μm), and 130–215 (~50–75 μm). The spectral bands in both regions are sensitive to the type of cation present because the polarizing power is related to the band center for many of the spectral features. Band assignments were confirmed for many of the spectral features due to opposing trends in vibrational energies for the ClO 4 – and H 2 O groups connected to different octahedral cations. Differential scanning calorimetry (DSC) data show variable patterns of water loss and thermal decomposition temperatures for perchlorates with different cations, consistent with changes in spectral features measured under varying hydration conditions. Results of the DSC analyses indicate that the bond energies of H 2 O in perchlorates are different for each cation and hydration state. Structural parameters are available for Mg perchlorates ( Robertson and Bish 2010 ) and the changes in structure due to hydration state are consistent with DSC parameters and spectral features. Analyses of changes in the Mg perchlorate structures with H 2 O content inform our understanding of the effects of hydration on other perchlorates, for which the specific structures are less well defined. Spectra of the hydrated Fe 2+ and Fe 3+ perchlorates changed significantly upon heating to 100 °C or measurement under low-moisture conditions indicating that they are less stable than other perchlorates under dehydrated conditions. The perchlorate abundances observed by Phoenix and MSL are likely too low to be identified from orbit by CRISM, but may be sufficient to be identifiable by a VNIR imager on a future rover.