¹Jeffrey R. Johnson et al. (>10)*
American Mineralogist 101, 1501-1514 Link to Article [doi:10.2138/am-2016-5553]
¹Applied Physics Laboratory, Johns Hopkins University, 11101 Johns Hopkins Road 200-W230 Laurel, Maryland 20723-6005, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website
Copyright: The Mineralogical Society of America

Relative reflectace point spectra (400–840 nm) were acquired by the Chemistry and Camera (ChemCam) instrument on the Mars Science Laboratory (MSL) rover Curiosity in passive mode (no laser) of drill tailings and broken rock fragments near the rover as it entered the lower reaches of Mt. Sharp and of landforms at distances of 2–8 km. Freshly disturbed surfaces are less subject to the spectral masking effects of dust, and revealed spectral features consistent with the presence of iron oxides and ferric sulfates. We present the first detection on Mars of a ~433 nm absorption band consistent with small abundances of ferric sulfates, corroborated by jarosite detections by the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument in the Mojave, Telegraph Peak, and Confidence Hills drilled samples. Disturbed materials near the Bonanza King region also exhibited strong 433 nm bands and negative near-infrared spectral slopes consistent with jarosite. ChemCam passive spectra of the Confidence Hills and Mojave drill tailings showed features suggestive of the crystalline hematite identified by CheMin analyses. The Windjana drill sample tailings exhibited flat, low relative reflectance spectra, explained by the occurrence of magnetite detected by CheMin. Passive spectra of Bonanza King were similar, suggesting the presence of spectrally dark and neutral minerals such as magnetite. Long-distance spectra of the “Hematite Ridge” feature (3–5 km from the rover) exhibited features consistent with crystalline hematite. The Bagnold dune field north of the Hematite Ridge area exhibited low relative reflectance and near-infrared features indicative of basaltic materials (olivine, pyroxene). Light-toned layers south of Hematite Ridge lacked distinct spectral features in the 400–840 nm region, and may represent portions of nearby clay minerals and sulfates mapped with orbital near-infrared observations. The presence of ferric sulfates such as jarosite in the drill tailings suggests a relatively acidic environment, likely associated with flow of iron-bearing fluids, associated oxidation, and/or hydrothermal leaching of sedimentary rocks. Combined with other remote sensing data sets, mineralogical constraints from ChemCam passive spectra will continue to play an important role in interpreting the mineralogy and composition of materials encountered as Curiosity traverses further south within the basal layers of the Mt. Sharp complex.

¹Kathleen C. Benison
American Mineralogist 101, 1499-1500 Link to Article [DOI: 10.2138/am-2016-5802]
¹Department of Geology and Geography, West Virginia University, Morgantown, West Virginia 26506, U.S.A.
Copyright: The Mineralogical Society of America

Identification of minerals on the surface of Mars is critical to understanding the geological history of our neighbor planet. In this issue of American Mineralogist, Ehlmann et al. report their discovery of alunite [KAl3(SO4)2(OH)6] in Cross Crater on Mars. Because terrestrial alunite forms from Al-rich acid sulfate waters, these results strongly suggest the past presence of Al-rich acid saline martian waters.

¹John F. Pernet-Fisher
American Mineralogist 101, 1497-1498 Link to Article [DOI: 10.2138/am-2016-5790]
¹School of Earth, Atmospheric, and Environmental Sciences, University of Manchester, Manchester M13 2PL, U.K.
Copyright: The Mineralogical Society of America

Earth-like δD values reported from lunar mare-basalt apatites have typically been interpreted to reflect the intrinsic isotopic composition of lunar-mantle water. New data indicates that some of these basalts are also characterized by having experienced a slow cooling history after their emplacement onto the lunar surface. This suggests that these basalts may have experienced metasomatism by fluxes generated during the degassing of the lunar regolith induced by the long-duration, high-temperature residence times of overlying basalts.

^1,4A. Jambon, ²V. Sautter, ³J-A. Barrat, ⁵J. Gattacceca, ⁵P. Rochette, ⁴O. Boudouma, ^1,4D. Badia, ^5,6B. Devouard
Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.06.032]
¹Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France
²Museum National d’Histoire Naturelle and UPMC Univ Paris 06, IMPMC, UMR7590 75005 Paris, France
³Université de Brest, CNRS UMR 6538 (Domaines Océaniques), I.U.E.M., Place Nicolas Copernic, 29280 Plouzané, France
⁴CNRS, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France
⁵Aix-Marseille Université, CNRS, CEREGE UM 34, F-13545 Aix-en-Provence cedex 4, France
⁶Université Blaise Pascal, CNRS, Laboratoire Magmas et Volcans UMR 6524, 5 rue Kessler, F-63000 Clermont-Ferrand, France
Copyright Elsevier

Northwest Africa 5790, the latest nakhlite find, is composed of 58 vol.% augite, 6% olivine and 36% vitrophyric intercumulus material. Its petrology is comparable to previously discovered nakhlites but with key differences: (1) Augite cores display an unusual zoning between Mg# 54 and 60; (2) Olivine macrocrysts have a primary Fe-rich core composition (Mg#= 35); (3) the modal proportion of mesostasis is the highest ever described in a nakhlite; (4) It is the most magnetite-rich nakhlite, together with MIL 03346, and exhibits the least anisotropic fabric. Complex primary zoning in cumulus augite indicates resorption due to complex processes such as remobilization of former cumulates in a new magma batch. Textural relationships indicate unambiguously that olivine was growing around resorbed augite, and that olivine growth was continuous while pyroxene growth resumed at a final stage. Olivine core compositions (Mg#= 35) are out of equilibrium with the augite core compositions (Mg# 60-63) and with the previously inferred nakhlite parental magma (Mg#= 29). The presence of oscillatory zoning in olivine and augite precludes subsolidus diffusion that could have modified olivine compositions. NWA 5790 evidences at least two magma batches before eruption, with the implication that melt in equilibrium with augite cores was never in contact with olivine. Iddingsite is absent.

Accordingly, the previous scenarios for nakhlite petrogenesis must be revised. The first primary parent magmas of nakhlites generated varied augite cumulates at depth (Mg# 66 to 60) as they differentiated to different extents. A subsequent more evolved magma batch entrained accumulated augite crystals to the surface where they were partly resorbed while olivine crystallized. Trace element variations indicate unambiguously that they represent consanguineous but different magma batches. The compositional differences among the various nakhlites suggest a number of successive lava flows. To account for all observations we propose a petrogenetic model for nakhlites based on several (at least three) thick flows. Although NWA5790 belongs to the very top of one flow, it should come from the lowest flow sampled, based on the lack of iddingsite.

¹Paul D. Asimow, ²Chaney Lin, ^3,4Luca Bindi, ¹Chi Ma, ^5,6Oliver Tschauner, ⁷Lincoln S. Hollister,⁸Paul J. Steinhardt
Proceedings of the National Academy of Sciences 113 7077–7081 Link to Article [doi: 10.1073/pnas.1600321113]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125;
²Department of Physics, Princeton University, Princeton, NJ 08544;
³Dipartimento di Scienze della Terra, Università degli Studi di Firenze, I-50121 Firenze, Italy;
⁴Consiglio Nazionale delle Ricerche–Istituto di Geoscienze e Georisorse, Sezione di Firenze, I-50121 Firenze, Italy;
⁵Department of Geoscience, University of Nevada, Las Vegas, NV 89154;
⁶High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89154;
⁷Department of Geosciences, Princeton University, Princeton, NJ 08544;
⁸Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544

We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe2+0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68–73Fe11–16Cu10–12Cr1–4Ni1–2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

¹Richard V. Morris et al. (>10)*
Proceedings of the National Academy of Sciences (2016) 113 7071-7076 Link to Article [doi:10.1073/pnas.1607098113]
¹NASA Johnson Space Center, Houston, TX 77058
*Find the extensive, full author and affiliation list on the publishers Website

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.