Bishop, J. L. Chapter 3 – Remote Detection of Phyllosilicates on Mars and Implications for Climate and Habitability. in (eds. Cabrol, N. A. & Grin, E. A. B. T.-F. H. to L. on M.) 37–75 (Elsevier, 2018). https://doi.org/10.1016/B978-0-12-809935-3.00003-7.
Schwertmann, U. & Murad, E. Effect of pH on the Formation of Goethite and Hematite from Ferrihydrite. Clays Clay Min. 31, 277–284 (1983).
Cornell, R. M. & Schwertmann, U. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses (Wiley, 2003). https://doi.org/10.1002/3527602097.
Jambor, J. L. & Dutrizac, J. E. Occurrence and Constitution of Natural and Synthetic Ferrihydrite, a Widespread Iron Oxyhydroxide. Chem. Rev. 98, 2549–2586 (1998).
Sagan, C., Phaneuf, J. P. & Ihnat, M. Total Reflection Spectrophotometry and Thermogravimetric Analysis of Simulated Martian Surface Materials. Icarus 4, 43–61 (1965).
Adams, J. B. & McCord, T. B. Mars: Interpretation of spectral reflectivity of light and dark regions. J. Geophys. Res. 74, 4851–4856 (1969).
Dollfus, A. Étude des planètes par la polarisation de leur lumière. Suppl. aux. Ann. d.’Astrophysique 4, 3–114 (1957).
Sharonov, V. ~V. A Lithological Interpretation of the Photometric and Colorimetric Studies of Mars. Sov. Astron. 5, 199 (1961).
Morris, R. V. et al. Evidence for pigmentary hematite on Mars based on optical, magnetic, and Mossbauer studies of superparamagnetic (nanocrystalline) hematite. J. Geophys. Res. Solid Earth 94, 2760–2778 (1989).
Bell, J. F. III, McCord, T. B. & Owensby, P. D. Observational evidence of crystalline iron oxides on Mars. J. Geophys. Res. Solid Earth 95, 14447–14461 (1990).
Bibring, J. P. et al. Global mineralogical and aqueous Mars history derived from OMEGA/Mars express data. Science 312, 400–404 (2006).
Pimentel, G. C., Forney, P. B. & Herr, K. C. Evidence about hydrate and solid water in the Martian surface from the 1969 Mariner Infrared Spectrometer. J. Geophys. Res. 79, 1623–1634 (1974).
Murchie, S. et al. Spatial Variations in the Spectral Properties of Bright Regions on Mars. Icarus 105, 454–468 (1993).
Jouglet, D. et al. Hydration state of the Martian surface as seen by Mars Express OMEGA: 1. Analysis of the 3 μm hydration feature. J. Geophys. Res. Planets 112, 1–20 (2007).
Milliken, R. E. et al. Hydration state of the Martian surface as seen by Mars Express OMEGA: 2. H2O content of the surface. J. Geophys. Res. Planets 112, 1–15 (2007).
Zent, A. P. & Quinn, R. C. Measurement of H2O adsorption under Mars-like conditions: Effects of adsorbent heterogeneity. J. Geophys. Res. Planets 102, 9085–9095 (1997).
Audouard, J. et al. Water in the Martian regolith from OMEGA/Mars Express. J. Geophys. Res. Planets 119, 1969–1989 (2014).
Murchie, S. L. et al. Visible to Short-Wave Infrared Spectral Analyses of Mars from Orbit Using CRISM and OMEGA. in Remote Compositional Analysis: Techniques for Understanding Spectroscopy, Mineralogy, and Geochemistry of Planetary Surfaces (eds. Bell I. I. I., J. F., Bishop, J. L. & Moersch, J. E.) 453–483 (Cambridge University Press, 2019). https://doi.org/10.1017/9781316888872.025.
Bishop, J. L., Pieters, C. M., Hiroi, T. & Mustard, J. F. Spectroscopic analysis of Martian meteorite Allan Hills 84001 powder and applications for spectral identification of minerals and other soil components on Mars. Meteorit. Planet. Sci. 33, 699–707 (1998).
Bishop, J. L. Visible and Near-Infrared Reflectance Spectroscopy. in Remote Compositional Analysis (eds. Bell III J. F., Bishop, J. L. & Moersch, J. E.) 68–101 (Cambridge University Press, 2019). https://doi.org/10.1017/9781316888872.006.
Beck, P. et al. A Noachian source region for the “Black Beauty” meteorite, and a source lithology for Mars surface hydrated dust? Earth Planet. Sci. Lett. 427, 104–111 (2015).
Morris, R. V. et al. Mössbauer mineralogy of rock, soil, and dust at Meridiani Planum, Mars: Opportunity’s journey across sulfate-rich outcrop, basaltic sand and dust, and hematite lag deposits. J. Geophys. Res. Planets 111, E12S15 (2006).
Morris, R. V. et al. Mössbauer mineralogy of rock, soil, and dust at Gusev crater, Mars: Spirit’s journey through weakly altered olivine basalt on the plains and pervasively altered basalt in the Columbia Hills. J. Geophys. Res. Planets 111, E02S13 (2006).
Morris, R. V. & Klingelhöfer, G. Iron mineralogy and aqueous alteration on Mars from the MER Mössbauer spectrometers. in The Martian Surface: Composition, Mineralogy and Physical Properties (ed. Bell, J.) 339–365 (Cambridge University Press, 2008).
Murad, E. & Schwertmann, U. The Möessbauer spectrum of ferrihydrite and its relations to those of other iron oxides. Am. Mineral. 65, 1044–1049 (1980).
Coey, J. M. D. Amorphous solids: a review of the applications of the Mössbauer effect. J. Phys. Colloq. 35, C6-89–C6-105 (1974).
Yen, A. S. et al. An integrated view of the chemistry and mineralogy of martian soils. Nature 436, 49–54 (2005).
Ming, D. W., Morris, R. V., Clark, B. C. The Martian Surface. Aqueous alteration on Mars (Cambridge University Press, 2008). https://doi.org/10.1017/CBO9780511536076.
Madsen, M. B. et al. Overview of the magnetic properties experiments on the Mars Exploration Rovers. J. Geophys. Res. Planets 114, E06S90 (2009).
Goetz, W. et al. Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust. Nature 436, 62–65 (2005).
Madsen, M. B. et al. The magnetic properties experiments on Mars Pathfinder. J. Geophys. Res. Planets 104, 8761–8779 (1999).
Meslin, P.-Y. et al. Soil Diversity and Hydration at Gale Crater. Mars. Sci. 341, 1–9 (2013).
Lasue, J. et al. Martian Eolian Dust Probed by ChemCam. Geophys. Res. Lett. 45, 10,968–10,977 (2018).
Rapin, W. et al. An interval of high salinity in ancient Gale crater lake on Mars. Nat. Geosci. 12, 889–895 (2019).
David, G. et al. Evidence for Amorphous Sulfates as the Main Carrier of Soil Hydration in Gale Crater, Mars. Geophys. Res. Lett. 49, e2022GL098755 (2022).
Bish, D. L. et al. X-ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest at Gale Crater. Science 341, 1238932 (2013).
Blake, D. F. et al. Curiosity at Gale Crater, Mars: Characterization and Analysis of the Rocknest Sand Shadow. Science 341, (2013).
Achilles, C. N. et al. Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars. J. Geophys. Res. Planets 122, 2344–2361 (2017).
Berger, J. A. et al. A global Mars dust composition refined by the Alpha-Particle X-ray Spectrometer in Gale Crater. Geophys. Res. Lett. 43, 67–75 (2016).
McLennan, S. & Taylor, S. R. Planetary Crusts: Their Composition, Origin and Evolution. Cambridge Planetary Science (Cambridge University Press, 2008). https://doi.org/10.1017/CBO9780511575358.
Gellert, R. & Yen, A. S. Elemental Analyses of Mars from Rovers Using the Alpha-Particle X-Ray Spectrometer. in Remote Compositional Analysis: Techniques for Understanding Spectroscopy, Mineralogy, and Geochemistry of Planetary Surfaces (eds. Bishop, J. L., Bell III J. F. & Moersch, J. E.) 555–572 (Cambridge University Press, 2019). https://doi.org/10.1017/9781316888872.030.
Leshin, L. A. et al. Volatile, Isotope, and Organic Analysis of Martian Fines with the Mars Curiosity Rover. Science. 341, 1238937 (2013).
Thomas, N. et al. The Colour and Stereo Surface Imaging System (CaSSIS) for the ExoMars Trace Gas Orbiter. Space Sci. Rev. 212, 1897–1944 (2017).
Bishop, J. L., Pieters, C. & Burns, R. G. Reflectance and Mössbauer spectroscopy of ferrihydrite-montmorillonite assemblages as Mars soil analog materials. Geochim. Cosmochim. Acta 57, 4583–4595 (1993).
Bishop, J. L. et al. Reflectance Spectroscopy of Ferric Sulfate-Bearing Montmorillonites as Mars Soil Analog Materials. Icarus 117, 101–119 (1995).
Bell, J. F. et al. Mineralogic and compositional properties of Martian soil and dust: Results from Mars Pathfinder. J. Geophys. Res. Planets 105, 1721–1755 (2000).
Johnson, J. R. et al. ChemCam passive reflectance spectroscopy of surface materials at the Curiosity landing site, Mars. Icarus 249, 74–92 (2015).
Ruff, S. W. & Christensen, P. R. Bright and dark regions on Mars: Particle size and mineralogical characteristics based on Thermal Emission Spectrometer data. J. Geophys. Res. Planets 107, 2-1-2-22 (2002).
Sherman, D. M., Burns, R. G. & Burns, V. M. Spectral characteristics of the iron oxides with application to the Martian bright region mineralogy. J. Geophys. Res. Solid Earth 87, 10169–10180 (1982).
Morris, R. V. et al. Spectral and other physicochemical properties of submicron powders of hematite (α-Fe2O3), maghemite (γ-Fe2O3), magnetite (Fe3O4), goethite (α-FeOOH), and lepidocrocite (γ-FeOOH). J. Geophys. Res. Solid Earth 90, 3126–3144 (1985).
Burns, R. G. Mineralogical Applications of Crystal Field Theory. Cambridge Topics in Mineral Physics and Chemistry (Cambridge University Press, 1993). https://doi.org/10.1017/CBO9780511524899.
Sklute, E. C. et al. Spectral and morphological characteristics of synthetic nanophase iron (oxyhydr)oxides. Phys. Chem. Miner. 45, 1–26 (2018).
Schwertmann, U. & Cornell, R. M. Iron Oxides in the Laboratary (Wiley-VCH Verlag GmbH, 2000). https://doi.org/10.1002/9783527613229.
Dehouck, E., McLennan, S. M., Sklute, E. C. & Dyar, M. D. Stability and fate of ferrihydrite during episodes of water/rock interactions on early Mars: An experimental approach. J. Geophys. Res. Planets 122, 358–382 (2017).
McSween, H. Y. & Keil, K. Mixing relationships in the Martian regolith and the composition of globally homogeneous dust. Geochim. Cosmochim. Acta 64, 2155–2166 (2000).
Viviano, C. E. et al. Composition of Amazonian volcanic materials in Tharsis and Elysium, Mars, from MRO/CRISM reflectance spectra. Icarus 328, 274–286 (2019).
Fischer, E. M. & Pieters, C. M. The Continuum Slope of Mars: Bidirectional Reflectance Investigations and Applications to Olympus Mons. Icarus 102, 185–202 (1993).
Bridges, N. T. et al. Aeolian bedforms, yardangs, and indurated surfaces in the Tharsis Montes as seen by the HiRISE Camera: Evidence for dust aggregates. Icarus 205, 165–182 (2010).
Scheinost, A. C., Chavernas, A., Barrón, V. & Torrent, J. Use and Limitations of Second-Derivative Diffuse Reflectance Spectroscopy in the Visible to Near-Infrared Range to Identify and Quantify Fe Oxide Minerals in Soils. Clays Clay Min. 46, 528–536 (1998).
Carlson, L. & Schwertmann, U. Natural ferrihydrites in surface deposits from Finland and their association with silica. Geochim. Cosmochim. Acta 45, 421–429 (1981).
Sassi, M. & Rosso, K. M. Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles. ACS Earth Sp. Chem. 3, 70–78 (2019).
Pommerol, A., Schmitt, B., Beck, P. & Brissaud, O. Water sorption on martian regolith analogs: Thermodynamics and near-infrared reflectance spectroscopy. Icarus 204, 114–136 (2009).
Bishop, J. L. & Pieters, C. M. Low-temperature and low atmospheric pressure infrared reflectance spectroscopy of Mars soil analog materials. J. Geophys. Res. Planets 100, 5369–5379 (1995).
Guinness, E. A. Spectral Properties (0.40 to 0.75 Microns) of Soils Exposed at the Viking 1 Landing Site. J. Geophys. Res. 86, 7983–7992 (1981).
Johnson, J. R. et al. Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 4. Final mission observations. Icarus 357, 114261 (2021).
Schröder, S. E. et al. Laboratory observations and simulations of phase reddening. Icarus 239, 201–216 (2014).
Guzewich, S. D., Smith, M. D. & Wolff, M. J. The vertical distribution of Martian aerosol particle size. J. Geophys. Res. Planets 119, 2694–2708 (2014).
Pike, W. T. et al. Quantification of the dry history of the Martian soil inferred from in situ microscopy. Geophys. Res. Lett. 38, L24201 (2011).
Pieczara, G., Manecki, M., Rzepa, G., Borkiewicz, O. & Gaweł, A. Thermal stability and decomposition products of p-doped ferrihydrite. Mater. (Basel) 13, 1–16 (2020).
Stanjek, H. & Weidler, P. G. The effect of dry heating on the chemistry, surface area, and oxalate solubility of synthetic 2-line and 6-line ferrihydrites. Clay Min. 27, 397–411 (1992).
Haberle, R. M. Estimating the power of Mars’ greenhouse effect. Icarus 223, 619–620 (2013).
Sassi, M. & Rosso, K. M. Ab Initio Evaluation of Solid-State Transformation Pathways from Ferrihydrite to Goethite. ACS Earth Sp. Chem. 6, 800–809 (2022).
Schwertmann, U., Stanjek, H. & Becher, H.-H. Long-term in vitro transformation of 2-line ferrihydrite to goethite/hematite at 4, 10, 15 and 25 °C. Clay Min. 39, 433–438 (2004).
Das, S., Hendry, M. J. & Essilfie-Dughan, J. Transformation of Two-Line Ferrihydrite to Goethite and Hematite as a Function of pH and Temperature. Environ. Sci. Technol. 45, 268–275 (2011).
Cornell, R. M. & Schwertmann, U. Influence of Organic Anions on the Crystallization of Ferrihydrite. Clays Clay Min. 27, 402–410 (1979).
Lee, S. & Xu, H. One-Step Route Synthesis of Siliceous Six-Line Ferrihydrite: Implication for the Formation of Natural Ferrihydrite. ACS Earth Sp. Chem. 3, 503–509 (2019).
Paige, C. R., Snodgrass, W. J., Nicholson, R. V., Scharer, J. M. & He, Q. H. The effect of phosphate on the transformation of ferrihydrite into crystalline products in alkaline media. Water Air. Soil Pollut. 97, 397–412 (1997).
Fairén, A. G. A cold and wet Mars. Icarus 208, 165–175 (2010).
Rampe, E. B. et al. A mineralogical study of glacial flour from Three Sisters, Oregon: An analog for a cold and icy early Mars. Earth Planet. Sci. Lett. 584, 117471 (2022).
Klingelhöfer, G. et al. Jarosite and Hematite at Meridiani Planum from Opportunity’s Mössbauer Spectrometer. Science 306, 1740–1745 (2004).
Rampe, E. B. et al. Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars. Earth Planet. Sci. Lett. 471, 172–185 (2017).
Morrison, S. M. et al. Expanded Insights into Martian Mineralogy: Updated Analysis of Gale Crater’s Mineral Composition via CheMin Crystal Chemical Investigations. Minerals 14 at https://doi.org/10.3390/min14080773 (2024).
Ehlmann, B. L. et al. Discovery of alunite in Cross crater, Terra Sirenum, Mars: Evidence for acidic, sulfurous waters. Am. Mineral. 101, 1527–1542 (2016).
Bishop, J. L. & Murad, E. Spectroscopic and geochemical analyses of ferrihydrite from springs in Iceland and applications to Mars. Volcano–Ice Interaction on Earth and Mars at https://doi.org/10.1144/GSL.SP.2002.202.01.18 (2002).
Janney, D. E., Cowley, J. M. & Buseck, P. R. Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite. Clays Clay Min. 48, 111–119 (2000).
Schindler, M., Michel, S., Batcheldor, D. & Hochella, M. F. A nanoscale study of the formation of Fe-(hydr)oxides in a volcanic regolith: Implications for the understanding of soil forming processes on Earth and Mars. Geochim. Cosmochim. Acta 264, 43–66 (2019).
Childs, C. W. & Wilson, A. D. Iron oxide minerals in soils of the Ha’apai group, Kingdom of Tonga. Soil Res. 21, 489–503 (1983).
Childs, C. W., Matsue, N. & Yoshinaga, N. Ferrihydrite in volcanic ash soils of Japan. Soil Sci. Plant Nutr. 37, 299–311 (1991).
Childs, C. W. & Parfitt, R. L. Weighted mean concentrations of minerals in New Zealand soils. 2. Allophane/imogolite. New Zeal. Soil Bur. Sci. Rep. 82, 20 (1987).
Parfitt, R. L., Childs, C. W. & Eden, D. N. Ferrihydrite and allophane in four Andepts from Hawaii and implications for their classification. Geoderma 41, 223–241 (1988).
Bishop, J. L. et al. Surface clay formation during short-term warmer and wetter conditions on a largely cold ancient Mars. Nat. Astron. 2, 206–213 (2018).
Wordsworth, R. et al. A coupled model of episodic warming, oxidation and geochemical transitions on early Mars. Nat. Geosci. 14, 127–132 (2021).
Ehlmann, B. L. & Edwards, C. S. Mineralogy of the Martian Surface. Annu. Rev. Earth Planet. Sci. 42, 291–315 (2014).
Carr, M. H. & Head, J. W. Geologic history of Mars. Earth Planet. Sci. Lett. 294, 185–203 (2010).
Rampe, E. B. et al. Allophane detection on Mars with Thermal Emission Spectrometer data and implications for regional-scale chemical weathering processes. Geology 40, 995–998 (2012).
Huguenin, R. L. Photostimulated oxidation of magnetite: 1. Kinetics and alteration phase identification. J. Geophys. Res. 78, 8481–8493 (1973).
Lewis, D. G. Transformations induced in ferrihydrite by oven-drying. Z. f.ür. Pflanzenernährung und Bodenkd. 155, 461–466 (1992).
Burns, R. G. Rates and mechanisms of chemical weathering of ferromagnesian silicate minerals on Mars. Geochim. Cosmochim. Acta 57, 4555–4574 (1993).
Mustard, J. F. et al. Olivine and Pyroxene Diversity in the Crust of Mars. Science 307, 1594–1597 (2005).
Hurowitz, J. A., Fischer, W. W., Tosca, N. J. & Milliken, R. E. Origin of acidic surface waters and the evolution of atmospheric chemistry on early Mars. Nat. Geosci. 3, 323–326 (2010).
Lundgreen, B., Jensen, H. G., Knudsen, J. M., Olsen, M. & Vistisen, L. Photostimulated oxidation of Fe2+ (aq): a Mars simulation experiment studied by Mössbauer spectroscopy. Phys. Scr. 39, 670 (1989).
Tabata, H., Sekine, Y., Kanzaki, Y. & Sugita, S. An experimental study of photo-oxidation of Fe(II): Implications for the formation of Fe(III) (hydro)oxides on early Mars and Earth. Geochim. Cosmochim. Acta 299, 35–51 (2021).
Chevrier, V. et al. Iron weathering products in a CO2+(H2O or H2O2) atmosphere: Implications for weathering processes on the surface of Mars. Geochim. Cosmochim. Acta 70, 4295–4317 (2006).
Chevrier, V., Rochette, P., Mathé, P. E. & Grauby, O. Weathering of iron-rich phases in simulated Martian atmospheres. Geology 32, 1033–1036 (2004).
Gasda, P. J. et al. Manganese-Rich Sandstones as an Indicator of Ancient Oxic Lake Water Conditions in Gale Crater, Mars. J. Geophys. Res. Planets 129, e2023JE007923 (2024).
Lanza, N. L. et al. Oxidation of manganese in an ancient aquifer, Kimberley formation, Gale crater, Mars. Geophys. Res. Lett. 43, 7398–7407 (2016).
Mitra, K., Moreland, E. L., Ledingham, G. J. & Catalano, J. G. Formation of manganese oxides on early Mars due to active halogen cycling. Nat. Geosci. 16, 133–139 (2023).
Mitra, K., Moreland, E. L. & Catalano, J. G. Capacity of Chlorate to Oxidize Ferrous Iron: Implications for Iron Oxide Formation on Mars. Minerals 10, https://doi.org/10.3390/min10090729 (2020).
Sultana, R., Poch, O., Beck, P., Schmitt, B. & Quirico, E. Visible and near-infrared reflectance of hyperfine and hyperporous particulate surfaces. Icarus 357, 114141 (2021).
Pommerol, A. et al. The SCITEAS experiment: Optical characterizations of sublimating icy planetary analogues. Planet. Space Sci. 109–110, 106–122 (2015).
Pommerol, A. et al. In-flight radiometric calibration of the ExoMars TGO Colour and Stereo Surface Imaging System. Planet. Space Sci. 105580, https://doi.org/10.1016/j.pss.2022.105580 (2022).
Thomas, N. et al. Absolute calibration of the Colour and Stereo Surface Imaging System (CaSSIS). Planet. Space Sci. 211, 105394 (2022).
Valantinas, A. et al. CaSSIS Color and multi-angular observations of martian slope streaks. Planet. Space Sci. 209, 105373 (2021).
Valantinas, A. et al. Evidence for transient morning water frost deposits on the Tharsis volcanoes of Mars. Nat. Geosci. 17, 608–616 (2024).
Vincendon, M. Mars surface phase function constrained by orbital observations. Planet. Space Sci. 76, 87–95 (2013).
McCleese, D. J. et al. Mars Climate Sounder: An investigation of thermal and water vapor structure, dust and condensate distributions in the atmosphere, and energy balance of the polar regions. J. Geophys. Res. Planets 112, E05S06 (2007).
Pommerol, A. et al. Photometry and bulk physical properties of Solar System surfaces icy analogs: The Planetary Ice Laboratory at University of Bern. Planet. Space Sci. 59, 1601–1612 (2011).
Gunderson, K., Thomas, N. & Whitby, J. A. First measurements with the Physikalisches Institut Radiometric Experiment (PHIRE). Planet. Space Sci. 54, 1046–1056 (2006).
Pommerol, A. et al. Photometric properties of Mars soils analogs. J. Geophys. Res. Planets 118, 2045–2072 (2013).
Craig, M., Cloutis, E. ~A. & Mueller, T. ME and Mini-ME: Two Mars Environmental Simulation Chambers for Reflectance Spectroscopy. In 32nd Lunar and Planetary Science Conference, abstract #1368 (2001).
Hollandt, J., Becker, U., Paustian, W., Richter, M. & Ulm, G. New developments in the radiance calibration of deuterium lamps in the UV and VUV spectral range at the PTB. Metrologia 37, 563–566 (2000).
Kinch, K. M. et al. Radiometric Calibration Targets for the Mastcam-Z Camera on the Mars 2020 Rover Mission. Space Sci. Rev. 216, 141 (2020).
Poitras, J. T. et al. Mars analog minerals’ spectral reflectance characteristics under Martian surface conditions. Icarus 306, 50–73 (2018).
Cloutis, E. A. et al. Spectral reflectance properties of minerals exposed to simulated Mars surface conditions. Icarus 195, 140–168 (2008).
Valantinas, A. Bright and Dusty Regions of Mars: New Insights from Experiments and Orbital Color Imaging. Ph.D. thesis, Universität Bern https://boristheses.unibe.ch/id/eprint/5317 (2022).
Majzlan, J., Navrotsky, A. & Schwertmann, U. Thermodynamics of iron oxides: Part III. Enthalpies of formation and stability of ferrihydrite (∼Fe(OH)3), schwertmannite (∼FeO(OH)3/4(SO4)1/8), and ε-Fe2O3 1 1Associate editor: D. Wesolowski. Geochim. Cosmochim. Acta 68, 1049–1059 (2004).