Fugacity oxygen

As pointed out in the first section of this chapter, there are many different ways of representing the same fundamental variable—the oxidation state of a system. Of these alternatives, the oxygen fugacity is most commonly used in geochemistry, particularly at higher temperatures. [Pg.493]

This is a convenient parameter for a number of reasons. First, many oxidation reactions can be written to include molecular oxygen as a reactant, for example the reduction of hematite to magnetite. [Pg.493]

Assuming unit activity for the solids, the equilibrium constant for this reaction is simply [Pg.493]

To find the oxygen fugacity for pressures different from 1 bar, the standard states for the equilibrium constant (18.47) are most conveniently chosen as pure solids at T [Pg.493]

There is a simple, linear relationship between the two variables pe and Eh, which is evident in comparing the two defining equations [Pg.359]

3Fe203( ) + 2H+ + 2 e = 2Fe304( ) +H2O We will discuss the relative merits of the two methods a little more further on. [Pg.360]

The method of calculating log/o -pH boundaries is illustrated with three examples. All other boundaries are derived in the same way. Our examples include the boundaries for water stability and for coexisting minerals, as well [Pg.360]

Activities of Mn for three different positions of the solid-aqueous boundary [Pg.360]

For the water stability boundaries, the dissociation reaction of water is [Pg.361]

Oxygen fugacity The relationship betweeen /sj and foj can be derived from the... [Pg.47]

Sverjensky (1984) calculated the dependency of Eu +/Eu + in hydrothermal solution on /oj (oxygen fugacity), pH and temperature. According to his calculations and assuming temperature, pH and /oj for epidote-stage alteration of basalt and Kuroko ores (Shikazono, 1976), divalent Eu is considered to be dominant in the rocks and hydrothermal solution. Thus, it is reasonable to consider that Eu in the rocks was removed to hydrothermal solution under the relatively reduced condition more easily than the other REE which are all tiivalent state in hydrothermal solution. Thus, it is hkely that Eu is enriched in epidote-rich altered volcanic rocks. Probably Eu was taken up by the rocks from Eu-enriched hydrothermal solution which was generated by seawater-volcanic rock interaction at relatively low water/rock ratio. [Pg.59]

Oxygen fugacity (fot)- The /oj-pH diagrams (Figs. 1.90 and 1.91) were constructed at 200°C and 250°C based on the homogenization temperatures and electrum-sphalerite temperatures (Shikazono, 1985d). [Pg.129]

Shikazono, N. (1974a) Physicochemical environment and mechanism of volcanic hydrothermal ore deposition in Japan, with special reference to oxygen fugacity. J. Fac. Scl U. Tokyo, 19, 27-56. [Pg.285]

How would the reaction have proceeded if the oxygen fugacity had been fixed by equilibrium with the atmosphere To find out, we repeat the calculation, this time holding the oxygen fugacity constant... [Pg.205]

An interesting aspect of the calculation is that when oxidizing seawater mixes into the reduced hydrothermal fluid, the oxygen fugacity decreases (Fig. 22.4). The capacity of seawater to oxidize the large amount of hydrothermal H2S(aq) is limited by the supply of C>2(aq) in seawater, which is small. Given the reaction,... [Pg.330]

Fig. 22.4. Oxygen fugacity (top) and concentrations of the predominant sulfur species (bottom) during the mixing simulation shown in Figure 22.3. Decrease in the H2S(aq) concentration is mostly in response to dilution with seawater, rather than oxidation.

To see how contact with atmospheric oxygen might affect the reaction, we repeat the calculation, assuming this time that oxygen fugacity is fixed at its atmospheric level... [Pg.451]

In the two calculations (one including, the other excluding calcite), the resulting fluids differ considerably in composition. After reaction of 1 cm3 of pyrite at atmospheric oxygen fugacity, the compositions are... [Pg.455]

Equilibria 9.93 and 9.94 are similar to those proposed by Fincham and Richardson (1954) for native sulfur. According to these equilibria, the solute states of sulfur compounds depend on oxygen fugacity the total concentration of sulfur dissolved in the melt initially decreases with increasing /q, based on equation 9.93, and then increases again when equilibrium 9.94 becomes dominant. [Pg.640]

A Oxygen fugacity corresponding to the intrinsic oxygen partial pressure /o = P% ... [Pg.670]

Kj, = - K, [REEmJ + iirdREEMg]-" +, , MgVsi B Oxygen fugacity higher than the intrinsic oxygen partial pressure fo > Pq (13)... [Pg.670]

Effects of Oxygen Fugacity on the Solid/Liquid Distribution... [Pg.687]

Oxygen fugacity fo directly affects the redox states of trace elements in melts (see, for instance, equation 10.45). Figure 10.12 shows the effects of fo on the oxidation state of Ti and V in an Na2Si205 melt at T = 1085 °C, according to the... [Pg.687]

Figure 10,12 Effects of oxygen fugacity on oxidation state of Ti and V in Na2Si205 melt at r = 1085 °C (experimental data from Johnston, 1964, 1965, and Johnston and Chelko, 1966).

Figure 10.13 Effect of oxygen fugacity on conventional partition coefficient of Cr. (A) Olivine/liquid partitioning experimental data of Bird (1971), Weill and McKay (1975), Huebner et al. (1976), Lindstrom (1976), and McKay and Weill (1976). (B) Subcalcic py-roxene/liquid partitioning experimental data of Schreiber (1976). Reprinted from A.J. Irving, Geochimica et Cosmochimica Acta, 42, 743-770, copyright 1978, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.

Huebner I S. and Sato M. (1970). The oxygen fugacity-temperature relationships of manganese oxide and nickel oxide buffers. Amer. Mineral, 55 934-952. [Pg.837]

Speidel D. H. and Osborn E. F. (1967). Element distribution among coexisting phases in the system MgO-FeO-FeoO -SiOo as a function of temperature and oxygen fugacity. Amer. Mineral, 52 1139-1152. [Pg.855]

Walfe H. S. and Weill D. F. (1975). Electrical conductivity of magmatic liquid elfects of temperatures, oxygen fugacity and composition. Earth Planet. Sci. Letters, 28 254-260. [Pg.859]

Keywords chromitite chromite, IPGE, PGM, oxygen fugacity, Laser-Ablation ICP-MS... [Pg.197]

Ballhaus, C., Berry, R.F., Green, D.H. 1990. Oxygen fugacity controls in the Earth s upper mantle. Nature, 348, 437-440. [Pg.200]

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