Minerals troilite

Enthalpies are cited in kJ/mol at 25 CC and 1 bar. Note pyrrhodte is cited as an idealized FeS phase. In reality, pyrrhotite has a formula Fex-j S, where x ranges from 0 to 0.17. The pure FeS mineral, troilite, does not exist in nature on the Earth s surface and is found in meteorites. 

Ferrous sulphide, FeS, occurs in nature as the mineral troilite (see p. 23), which is found in nodules in the majority of meteorites containing iron. When crystalline it appears to belong to the hexagonal system, and has probably been formed in the presence of excess of iron.8 It may be obtained by the direct union of iron and sulphur at red heat. If the iron is m the form of filings and is intimately mixed with the sulphur, the mass becomes incandescent when once the reaction has been started. Synthetic iron disulphide, heated above 700° C., is converted into ferrous sulphide.9... 

For stable sulphur isotopes, the standard is an iron sulphide mineral (troilite) from the Canyon Diablo meteorite. It is known as CDT (Canyon Diablo troilite) and equation 1 becomes ... 

Iron(ll) sulfide, FeS, is the mineral troilite, known only to occur naturally in meteoritic (that is, extraterrestrial) iron. On the other hand, pyrite is a very common phase occurring in a wide variety of rocks and is an essential component of the rock type lapis lazuli, from which natural ultramarine (Tazurite) is extracted. Copperas, an important raw material used in the manufacture of synthetic iron oxide red pigments, forms from the breakdown of pyrite. 

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,... 

From a thermodynamic point of view, the transformation of graphite is accessible with the available experimental apparatuses, but it is kinetically impossible. Geological times, hundreds of years, are required for spontaneous formation of diamond in appropriate conditions, and kinetic factors prevent the observation of the reaction in any practical time scale. H. T. Hall has demonstrated that for graphite diamond conversion, carbon-carbon bonds must be broken in a solvent and on December 1954 realized the first synthesis of diamond, at approximately 2000 K and 10 GPa, in molten troilite (FeS) solvent, using a belt-type high-pressure-high-temperature apparatus [516-519]. Since then, many substances, minerals, and transition metals, in particular, have been... 

The winonaites are compositionally similar to silicate inclusions in some IAB irons (described below). They have chondritic compositions, and relict chondrules have been found in some meteorites. They consist of olivine, pyroxenes, plagioclase, metal, troilite, and other minor minerals (Benedix et al., 1998), and most have been recrystallized. Like the acapulcoites, they have experienced only small degrees of melting. 

If an internal isochron cannot be generated, a model age can be determined from the measured 207pb /206Pb of the sample and the assumed initial lead isotopic ratios. For studies of the early solar system, this initial lead composition is assumed to be that measured in troilite (FeS) from the Canyon Diablo meteorite. Troilite is a uranium-free mineral and its host meteorite formed very early in the history of the solar system. Because the U/Pb ratio of the solar system is low, the lead incorporated into the troilite should not have evolved significantly from the initial composition in the solar system. 

Troilite (FeS) is also a common mineral in chondrites. Chondrules sometimes have rims of troilite, which may be recondensates of evaporated sulfur from chondrule precursors. The recondensation behavior of sulfur onto chondrules would be different from that of moderately volatile alkali elements described above. During cooling, sulfur would not re-enter the melt because the chondrule melt would have solidified by the time sulfur began to recondense. Instead, sulfur would recondense as sulfide veneers around chondrules (Zanda et al. 1995) or as opaque assemblages... 

Many chondrules contain minor amounts of metals, sulfides, and oxides. These phases also occur as distinct grains and assemblages embedded in the chondrite matrix. The metallic mineral kamacite is a common chondrule component that contains significant amounts of minor elements such as cobalt, chromium, and phosphorus. Taenite is another alloy of iron and nickel. Sulfide minerals such as troilite, pyrrhotite, and pentlandite are also abundant in many chondrules. 

A double sulphide of iron and chromium, FeS.Cr2S3, occurs as the rare mineral daubreelite11 associated with troilite. It possesses a brilliant metallic lustre, is black in colour, but not magnetic. Density 5 0. 

Fig. 12. Fischer-Tropsch reaction at 1 atm is first-order in CO, with an activation energy of 27 kcal/ mole (Lancet, 1972). Rate in a flow system is 10 times faster than in the static system used here. Dashed line shows extrapolation to solar nebula, assuming that the rate is proportional to (PcoIIPhj) . Reaction proceeds at an undetectable rate when the Bruderheim L6 chondrite is used as a catalyst. Apparently the high-temperature minerals in this meteorite (olivine, orthopyroxene, troilite, and nickel-iron) do not catalyze the hydrogenation of CO. Thus CO can survive in the solar nebula down to 400 K, when catalytically active minerals first from (Fig. 1 and 10)...

Burbine et al. (2002) tested an extreme case of a possible composition for the surface of Mercury. They made spectral observations of enstatite achondrites (igneous meteorites composed almost entirely of pure MgSi03, with some accessory minerals and essentially no FeO). The spectral features of enstatite achondrites (aubrites see Chapter 1.05) are similar to those for Mercury, but lack the spectral reddening observed in spectra of Mercury and have an additional feature at 0.5 p.m caused by troilite (FeS). This reddening (visible to UV ratio) is the result of space weathering, in which FeO is reduced to very small grains of metallic iron. Thus, the reddening indicates that some FeO must be present on Mercury to produce the nanophase iron. Alternatively,... 

The production of protons is linked to the mineral stoichiometry. Up to one-quarter mole of the protons produced are derived from the oxidation of one mole of the iron-deficient form (x = 0.125), whereas no protons are produced from the stoichiometric form, which is troilite (x = 0). The release of protons can also result from the oxidation of the dissolved iron resulting from... 

The mineral pyrrhotite has a composition range extending from FeS to Fe 877S (" 7 8 name troilite is reserved for the... 

Experiments with Individual Minerals. Single mineral mounts in the heating-stage crucible yielded the expected products, that is, pyrite yielded pyrrhotite and troilite, calcite gave lime and carbon dioxide, and clays reacted under high temperature conditions to yield a silicate glass. 

The total abundance of each condensate is limited by the abundance of the least abundant element in the condensate. For example, the mineral schreiber-site Fe3P forms by reaction of P-bearing gases with Fe metal at about 1300 K and 10 4 bar total pressure. Phosphorus has an atomic abundance of 8,373 atoms, which is about 1% of the atomic abundance of iron. There are 3 Fe atoms in each molecule of schreibersite. Thus Fe3P formation consumes only 3% of the total iron abundance, while removing all phosphorus from the gas phase. Likewise, troilite formation removes all sulfur from the gas because its abundance is only 53% of that of iron, while unreacted Fe metal remains present at lower temperatures until it is consumed by formation of Fe-bearing oxides and silicates. 

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