Mackinawite

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

Farquhar ML, Chamock JM, Livens FR, Vaughun DJ (2002) Mechanisms of arsenic uptake from aqueous solution by interaction with goethite, lepidocrocite, mackinawite and pyrite as X-ray absorption spectroscopy study. Environ Sci Tecnol 36 1757-1762... 

Square metal nets are found in the tetragonal modifications of FeQ (Q=S, Se, Te) the Fe-Fe distances in the mackinawite modification of FeS are only 2.60 A.230 There are also metallic phases T1M2Q2 (M=Co, Cu Q=S, Se) and TlFe2Se2 that all adopt the ThCr2Si2 structure type, where the TM atoms form flat square nets with short M-M distances (2.65-2.75 A).232... 

We can expect the sulfide produced by the bacteria to react with the iron in solution to form mackinawite (FeS), a precursor to pyrite (FeS2). The mineral is not in the default thermodynamic database, so we add to the file the reaction... 

To run the simulation, we decouple acetate from carbonate, and sulfide from sulfate, and suppress the iron sulfide minerals pyrite and troilite (FeS), which are more stable than mackinawite, but unlikely to form. We set the fluid composition, including an amount of HS small enough to avoid significantly supersaturating mackinawite, and define the rate law for the sulfate reducers. The procedure in REACT is... 

To set up the simulation, we use the thermodynamic dataset from the calculation in Section 18.5, which was expanded to include mackinawite (FeS). As before, we suppress the iron sulfide minerals pyrite and troilite, and decouple acetate and methane from carbonate, and sulfide from sulfate. We set the aquifer to include a small amount of siderite, which serves as a sink for aqueous sulfide,... 

The HS formed further dissociates to (pK = 13.9). However in most submerged soils the concentration of Fe + in the soil solution is sufficient that virtually all is precipitated as amorphous ferrous sulfide and very small concentrations of H2S and HS remain in solution. The relations between the S04 -HS and Fe(OH)3-Fe " systems at neutral pH are shown in Figure 4.12. Amorphous ferrous sulfide may gradually crystallize as mackinawite (FeS). Under some circumstances pyrite is then formed, e.g. FeS(s) + S(s) FeS2(s), leading to potential acid sulfate soils (Section 7.3). 

Slowly reacts with water forming HCl (NIOSH, 1997). 1,1,1-Trichloroethane also was shown to react with a form of iron sulfide mineral, namely mackinawite (FeS(i x)). Complete removal of... 

Sulfides (pyrite, sphalerite, wurtzite, galena, greigite, mackinawite)... 

Many mineral species are known to be selectively crystallized by the presence of bacteria. Carbonate minerals, such as calcite, aragonite, hydroxycalcite, and siderite oxide minerals, such as magnetite and todorokite oxalate minerals, such as whewellite and weddellite sulfide minerals, such as pyrite, sphalerite, wurtzite, greigite, and mackinawite and other minerals, such as jarosite, iron-jarosite, and g3q>sum, are known to precipitate in the presence of bacteria. Therefore, investigations have been developed to analyze the formation of banded iron ore by the action of bacteria, and to analyze the ancient environmental conditions of the Earth through the study of fossilized bacteria. 

Wolthers, M., Charlet, L., van Der Weijden, C.H. et al. (2005) Arsenic mobility in the ambient sulfidic environment sorption of arsenic(V) and arsenic(III) onto disordered mackinawite. Geochimica et Cosmochimica Acta, 69(14), 3483-92. 

Bostick and Fendorf (2003), 918 performed detailed laboratory studies and concluded that arsenic could form surface precipitates on FeS (including troilite, pyrrhotite, and mackinawite) under anoxic conditions as shown in the following reaction ... 

Suspended solid surfaces (particles or colloids) in waters play a prominent role in controlling the concentration of dissolved trace elements. Most of these elements are eliminated by sedimentation after incorporation on to or into particles, generally by complexation with the surface sites. The most common inorganic particles and colloids are non-clay silicates (quartz, potash feldspar, plagioclase, opaline silica (diatoms)) clays (illite, smectite) carbonates (calcite, dolomite) Fe-Mn oxides (goethite, magnetite) phosphates (apatite) sulfides (mackinawite). Particles and colloids in a water body may be classified as a function of their origin ... 

In marine and lacustrine muds, the initial sulfide phase precipitated during early diagenesis is mackinawite (FeS09) which is subsequently converted to greigite (Fe3S4) and pyrite (FeS2) (85-89). This reaction path leads to the formation of framboidal pyrite (88.90). However, in salt marsh sediments under low pH and low sulfide ion activity conditions, direct precipitation of pyrite by reaction of ferrous iron with elemental sulfur without the formation of iron monosulfides as intermediates has been reported (85-87.89.91.92). This reaction is one possible pathway for the precipitation of pyrite as single crystals (89). 

In sediments, Fe sulfides are typically divided into the following two groups acid volatile sulfides (AVS), which are evolved via acid distillation and generally include amorphous forms [e.g., mackinawite (FeS), greigite (Fe3S4), and pyrrhotite (FeS)], and pyrite (FeS2). 

Morse, J.W., and Arakaki, T. (1993) Adsorption and coprecipitation of divalent metals with mackinawite (FeS). Geochim. Cosmochim. Acta 57, 3635-3640. 

Distribution of dissolved Fe(II), as well as in the case of dissolved Mn(II), is characterized by the increasing of its content in the redox zone and by formation of an intermediate maximum within the dissolved Mn(II) maximum. Fe(II) is oxidized rapidly in the presence of oxygen to Fe(III) that exists as oxides and hydroxides with low solubility. The dissolved Fe(II) appears at a = 16.2 kgm-3. Its concentration increases toward the maximum (about 0.3 pM at oq = 16.5-16.6 kgm 3), and then decreases to 0.05-0.07 pM at or = 16.8 kg m-3. The deep concentrations appear to be controlled by solubility with FeS (mackinawite) or Fe3S4 (greigite), even though FeS2 (pyrite) is more insoluble and is present in the water column [71]. 

Semiconductors are considered to be catalytic particles that contributed to the development of primitive metabolism. According to Wahtershauser life could have developed on the surface of iron sulphide minerals (eg mackinawite or pyrrhotite [FeS] or pyrite [FeS2]) [8], The chemoautotrophy theory is based on the reaction between iron sulphide and hydrogen sulphide, which acts as a reducing agent, whereas iron sulphide provides adsorption sites for substrates and acts as a catalyst (equation 10.1) ... 

Figure 10.2 Crystal structures of (a, b, c) natural iron and (d) zinc sulphides (a) greigite, (b) mackinawite, (c) smythite, and (d) sphalerite...

Lennie AR, Redfem SAT, Schofield PF, Vaughan DJ. Synthesis and Rietveld crystal structure refinement of mackinawite, tetragonal FeS. Miner Mag 1995 59 677-83. 

Fig. 7a-d. Idealised lepresentations of various layer types observed in non-commensurate layer structures (a) octahedral layer, MX2, (111) B1 type (b) galena-like half octahedral (square pyramidal) layer, MX, (100) B1 type (c) the valleriite-like tetrahedral layer, MX, (111) anti-C 1 type (d) the mackinawite-like tetrahedral layer, MX, (100) anti-Cl type... 

Fig. 10. Types of mackinawite-like layer A, in tochilinite I B, in Phases 1 and 2 of Organova et al. C, in tochilinite II D, in mackinawite, FeS. TTie layer is projected along the 4 axis fractionally occupied tetrahedra are stippled component cells are outlied...

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