D. E. Latta, A. Neumann, W. A. P. J. Premaratne and M. M. Scherer, Fe(II)-Fe(III) electron transfer in a clay mineral with low Fe content, ACS Earth and Space Chem, 2017, 1, 197–208 CrossRef CAS . Chang K (12 March 2013). "Mars Could Once Have Supported Life, NASA Says". The New York Times . Retrieved 12 March 2013. Other 2:1 clay types exist such as palygorskite (also known as attapulgite) and sepiolite, clays with long water channels internal to their structure. A. M. Jones, R. N. Collins, J. Rose and T. D. Waite, The effect of silica and natural organic matter on the Fe(II)-catalysed transformation and reactivity of Fe(III) minerals, Geochim. Cosmochim. Acta, 2009, 73, 4409–4422 CrossRef CAS . In the XAS samples, the sorbed fraction of Fe 2+ was higher at pH ∼8 than at pH ∼7 (Table S2 †). The amount of sorbed Fe 2+ also slightly increased with increasing equilibration time from day 1 to 30 (Table S2 and Fig. S3 †), e.g., by 0.02 mol Fe per kg clay at pH 7. This observation is consistent with findings by Zhu et al., 34 who observed an increase in Fe 2+ sorption to Syn-1 during 5 days at pH 7.5. Such increases of Fe 2+ sorption suggest that slow sorption processes were taking place. Possible mechanisms explaining slow sorption kinetics include dissolution and precipitation reactions on surfaces. 35–44

A. C. Senn, R. Kaegi, S. J. Hug, J. G. Hering, S. Mangold and A. Voegelin, Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: Interdependent effects of phosphate, silicate and Ca, Geochim. Cosmochim. Acta, 2015, 162, 220–246 CrossRef CAS . If a game has great components, it can elevate the experience to something next-level. Sometimes it can even save one that has a few bumps in its design. Not often. But sometimes. On the other hand, if a game has poor components, then that’s a real knife-edge moment. Keep it despite the bargain-basement bits? Or lose it and seek something similar but better furnished? Iron Investment For all oxic sorption samples, the position of the Fe K-edge was at 7127 eV ( Fig. 2), which corresponds to the oxidation state Fe( III) and is in line with Mössbauer data ( Fig. 2). Linear combination fitting (LCF) results for Fe K-edge EXAFS spectra are presented in Fig. 4 (also Tables S11 and S12 †). Oxidized sorption samples were well described ( R-factor < 2%) with 3 reference compounds: ferrihydrite (45–60%), Fe( III)-containing phyllosilicates (24–36%), and lepidocrocite (13–19%). Essentially, all oxic sorption samples transformed into the same secondary phases regardless of their equilibration conditions (pH, Fe concentration) and time (1 or 30 days) under anoxic conditions (Tables S11 and 12 †). Parts of the Fe( III)-containing phyllosilicates that have already formed under anoxic conditions were not affected by oxidation and remained as secondary phase after aeration. It was observed that the fraction of lepidocrocite formed was significantly lower for low Fe-loading samples compared to high Fe-loading samples. A. Voegelin, R. Kaegi, J. Frommer, D. Vantelon and S. J. Hug, Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy, Geochim. Cosmochim. Acta, 2010, 74, 164–186 CrossRef CAS . To investigate the sorption mechanism of Fe 2+ to Syn-1 by XAS further, an additional set of samples was prepared at pH 7 or 8 under anoxic conditions containing 5 g L −1 clay, 0.25 or 2.5 mM Fe 2+, and 50 mM CaCl 2. The high CaCl 2 concentration and pH values were selected to focus on sorption processes on edge surfaces, which are expected to dominate under these conditions. Furthermore, at pH < 8 the dissolved Fe 2+ concentrations in the suspensions were always below saturation with respect to Fe(OH) 2 (Table S1 †).X-ray absorption spectroscopy (XAS). The samples for XAS analysis were prepared by equilibrating Syn-1 (∼5 g L −1) with a Fe 2+ solution (0.25 and 2.5 mM) in 50 mM CaCl 2 to maintain similar conditions as in our previous experiments, but with higher solid concentrations suitable to facilitate XAS analysis. This set of samples was prepared to investigate the solid-phase speciation of Fe and the effects of equilibration time (1 and 30 days), pH (∼7 and ∼8), Fe-loading (0.05 and 0.5 mol Fe per kg clay), and oxidation. L. Bhattacharya and E. J. Elzinga, A comparison of the solubility products of layered Me(II)-Al(III) hydroxides based on sorption studies with Ni(II), Zn(II), Co(II), Fe(II), and Mn(II), Soil Syst., 2018, 2, 20 CrossRef CAS .

P. Gütlich, E. Bill and A. X. Trautwein, Mossbauer Spectroscopy and Transition Metal Chemistry: Fundamentals and Applications, Springer, 2011 Search PubMed . For the majority of the samples, the LCF significantly improved when an Fe( III)-containing clay mineral reference (SWy-2, containing 3 wt% Fe) was included as additional reference in the fits. Released Si from Syn-1 after 1 day equilibration between pH 6 and 10 amounted on average to ∼0.016 mmol Si per g clay compared to up to 8 times lower Si concentrations for anoxic sorption samples with Fe (see Fig. S6a and S7 †). This provides additional evidence that the released Si from Syn-1 was removed from solution upon addition of Fe, either by adsorption or incorporation into newly formed Fe phases. It has been suggested by Soltermann et al. 30 that Fe 2+ can be taken up by the clay minerals, leading to the formation of Fe-bearing clay minerals. Clay is a very fine-grained geologic material that develops plasticity when wet, but becomes hard, brittle and non–plastic upon drying or firing. [2] [3] [4] It is a very common material, [5] and is the oldest known ceramic. Prehistoric humans discovered the useful properties of clay and used it for making pottery. [6] The chemistry of clay, including its capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility. [7]A. M. Scheidegger, D. G. Strawn, G. M. Lamble and D. L. Sparks, The kinetics of mixed Ni-Al hydroxide formation on clay and aluminum oxide minerals: A time-resolved XAFS study, Geochim. Cosmochim. Acta, 1998, 62, 2233–2245 CrossRef CAS . Fig. 3 77 K Mössbauer spectra and fits of high Fe-loading solid samples. Syn-1 (1 g L −1) was reacted with 0.5 mM Fe 2+ (enriched in 57Fe) at pH ∼7 or ∼8 under anoxic conditions during 1 day (a and b). Anoxic samples were subsequently exposed to air for 1 day (c and d). Displayed pH values correspond to the pH measured at the end of the equilibration period for each sample. In all graphs, symbols represent data and red lines the model fits. Corresponding fitting parameters are summarized in Table S6. † The Fe( II) doublet is represented as green area and the Fe( III) doublet as orange area. Clay minerals can be classified as 1:1 or 2:1. A 1:1 clay would consist of one tetrahedral sheet and one octahedral sheet, and examples would be kaolinite and serpentinite. A 2:1 clay consists of an octahedral sheet sandwiched between two tetrahedral sheets, and examples are talc, vermiculite, and montmorillonite. The layers in 1:1 clays are uncharged and are bonded by hydrogen bonds between layers, but 2:1 layers have a net negative charge and may be bonded together either by individual cations (such as potassium in illite or sodium or calcium in smectites) or by positively charged octahedral sheets (as in chlorites). [9] H. Funke, A. C. Scheinost and M. Chukalina, Wavelet analysis of extended x-ray absorption fine structure data, Phys. Rev. B: Condens. Matter Mater. Phys., 2005, 71, 094110 CrossRef . Natural clay minerals often contain Fe( II) and Fe( III) in their crystal lattice 11,12 and it has been shown that electrons can be transferred from ferrous iron to structural Fe( III). 13–18 Iron-free clay minerals are generally considered to be redox-inactive within the natural redox potential of soils. However, Géhin et al. 14 demonstrated that under strictly anoxic conditions Fe( II) was oxidized to Fe( III) on surfaces of clay minerals having very low iron contents. Potential electron acceptors in low-iron clay minerals could include trace Fe( III) impurities, other redox-active elements ( e.g., Ti), or hydrogen. 14 Following oxidation, the hydrolysis of Fe( III) may lead to the formation of oxyhydroxide clusters or precipitates on the clay mineral surface, as has been observed by many studies. 12,15,19,20 However, uncertainties still prevail about the ability of Fe-free clay mineral to induce electron transfer from adsorbed Fe( II) to the clay mineral, leading to the formation of adsorbed Fe( III). 19,21

A. Voegelin, A. C. Scheinost, K. Buhlmann, K. Barmettler and R. Kretzschmar, Slow formation and dissolution of Zn precipitates in soil - A combined column-transport and XAFS study, Environ. Sci. Technol., 2002, 36, 3749–3754 CrossRef CAS PubMed . A lower amount of lepidocrocite was formed in the low Fe-load samples, as direct oxidation of Fe 2+ in presence of elevated Si concentrations (high Si/Fe ratio in solution) may mainly precipitate as ferrihydrite. 73 However, only a small fraction of the sorbed Fe in the oxic samples was formed by direct oxidation of dissolved Fe 2+ for low Fe-loading samples equilibrated at pH ∼8 (between 7 and 12%, see Fig. S4 and S5 †) compared to samples equilibrated at pH ∼7 (between 60 and 65%, see Fig. S4 and S5 †). Nevertheless both low Fe-loading samples resulted in the presence of similar solid phases. The higher fraction of lepidocrocite observed in the high Fe-loading oxic samples as compared to the low Fe-loading samples may be due to the oxidation of dissolved Fe 2+ in the presence of a low Si/Fe ratio in solutions, which favors lepidocrocite formation over ferrihydrite or through the transformation of green rust into lepidocrocite. 66,73 Because only a small fraction of the sorbed Fe (up to 20%, see Fig. S4 and S5 †) was formed by direct oxidation of dissolved Fe 2+ in high Fe-loading samples, lepidocrocite was primarily formed from the transformation of Fe-phases precipitated under anoxic conditions.

Fundamentals of Soil Behavior, 3rd Edition James K. Mitchell, Kenichi Soga. ISBN 978-0-471-46302-3, Table 3.9.

a b c d Bailey SW (1980). "Summary of recommendations of AIPEA nomenclature committee on clay minerals". Am. Mineral. 65: 1–7. Like all phyllosilicates, clay minerals are characterised by two-dimensional sheets of corner-sharing SiO 4 tetrahedra or AlO 4 octahedra. The sheet units have the chemical composition (Al, Si) 3O 4. Each silica tetrahedron shares three of its vertex oxygen ions with other tetrahedra, forming a hexagonal array in two dimensions. The fourth oxygen ion is not shared with another tetrahedron and all of the tetrahedra "point" in the same direction; i.e. all of the unshared oxygen ions are on the same side of the sheet. These unshared oxygen ions are called apical oxygen ions. [20] A. N. Starcher, E. J. Elzinga and D. L. Sparks, Formation of a mixed Fe(II)-Zn-Al layered hydroxide: Effects of Zn co-sorption on Fe(II) layered hydroxide formation and kinetics, Chem. Geol., 2017, 464, 46–56 CrossRef CAS . K. Lagarec and D. G. Rancourt, Recoil − Mössbauer spectral analysis software for Windows., University of Ottawa, Ottawa, 1998 Search PubMed .S. Sengupta, P. K. Mukherjee, T. Pal and S. Shome, Nature and origin of arsenic carriers in shallow aquifer sediments of Bengal Delta, India, Environ. Geol., 2004, 45, 1071–1081 CrossRef CAS . C. A. Gorski, M. Aeschbacher, D. Soltermann, A. Voegelin, B. Baeyens, M. Marques Fernandes, T. B. Hofstetter and M. Sander, Redox properties of structural Fe in clay minerals. 1. Electrochemical quantification of electron-donating and -accepting capacities of smectites, Environ. Sci. Technol., 2012, 46, 9360–9368 CrossRef CAS PubMed . Honestly, these Iron Clays really have opened my eyes. Previously resistant to investing in accessories, I am now actually looking for games with the worst cardboard counters just so that I can revel in superior counter smugness! If you are fed up with cardboard coins lowering your fun level, I highly recommend investing in Iron Clays. After all, stunning counters are for life, not just for Christmas!