Solid solutions pyroxenes

Figure 13 Bulk compositions of aluminum-rich chondrules plotted in the system Al203-Mg2Si04-Ca2Si04 and projected from spinel (MgAl204). Mineral abbreviations An = anorthite, Grs = grossite, Cor = corundum, Cord = cordierite, Di = diopside, Fo = forsterite, Geh = gehlenite, Hib = hibonite, La = lamite, L = liquid, Mel = melilite solid solution. Mull = mullite. Mo = monticellite, Mw = merwinite. Per = periclase. Pyx = pyroxene solid solution, Saph = sapphirine (data from Bischoff and Keil (1984), Sheng et al. (1991), Huss et al.

Moore R. O. and Gurney J. J. (1985) Pyroxene solid solution in garnets included in diamond. Nature (London) 318(6046), 553-555. 

Pyroxenes are abundant natural metasilicates with chain-arranged Si04 tetrahedra. The most frequently arising monoclinic pyroxenes contain chains jointed laterally by cations Mg, and others. Their structure is analogous to that of diopside CaMgSi20 which constitutes the basis of a wide series of pyroxene solid solutions. 

The pyroxene solid solution is a desirable phase of petrositals its structure can be entered by various mono-, di- and trivalent cations. With this type ft is therefore possible to attain the so-called monomineral crystallization, i.e. formation of a single crystalline phase. 

The olivine projection is illustrated in Figure 3.27. This plane contains all the pyroxene solid solutions and the garnet solid solutions. The oUvine-plagiockse piercing point is the point at which the olivine plagioclase join cuts the CS-MS-A... 

The activities of FeO in solid solutions of FeO and MgO were obtained at 1100 ° and 1300 °C by Hahn and Muan (1962). The method was similar to that for the pyroxene solid solutions described above. Solid solutions of FeO and... 

Table V. Nomenclature for (Mg, Fe) Solid Solution Series of Olivines and Pyroxenes Treated in This Study...

The other mineral spectra shown are pyroxenes. The bronzite sample studied (Figure 10) is almost a member of the solid-solution series listed in Table V, although small amounts of Al and Ca are present. Consequently, it should be compared with the synthetic members of this series described below. Even in this natural mineral sample there is clear... 

The hosts for ACT and REE immobilization are phases with a fluorite-derived structure (cubic zirconia-based solid solutions, pyrochlore, zirco-nolite, murataite), and zircon. The REEs and minor ACTs may be incorporated in perovskite, monazite, apatite-britholite, and titanite. Perovskite and titanite are also hosts for Sr, whereas hollandite is a host phase for Cs and corrosion products. None of these ceramics is truly a single-phase material, and other phases such as silicates (pyroxene, nepheliiie, plagioclase), oxides (spinel, hibonite/loveringite, crichtonite), or phosphates may be present and incorporate some radionuclides and process contaminants. A brief description of the most important phases suitable for immobilization of ACTs and REEs is given below. 

Therefore, the true configurational entropy is 0.95 J/(deg. mole) lower than the maximum value as a result of Fe2+-Mg2+ ordering in the orthopyroxene structure. The cation ordering found in other members of the enstatite—ferrosilite series, as well as the synthetic Mg2+-Ni2+, Mg2+-Co2+ and Mg2+-Mn2+ pyroxenes (Ghose et al., 1975 Hawthorne and Ito, 1977), shows that most transition metal-bearing orthopyroxenes are not ideal solid-solutions. 

Saxena, S.K., 1969b. Silicate solid solutions and geothermometry. 2. Distribution of Fe " and Mg between coexisting olivine and pyroxene. Contrib. Mineral. Petrol., 22 147-156. 

Figure 2 Condensation of major rock-forming phases from a gas of solar composition (Anders and Grevesse, 1989) at a total pressure of 10 atm. This calculation was done with the best currently available internally consistent thermodynamic data for solid and gaseous phases and includes nonideal solid solution models for melilite, Ca-rich pyroxene, feldspar, and metal. This calculation is the same as the one shown in Yoneda and Grossman (1995, table 1...

Akaogi M. and Akimoto S. (1977) Pyroxene-garnet solid-solution equilibria in the systems Mg4Si40i2-Mg3Al2Si30i2 and Fe4Si40i2-Fe3Al2Si30i2 at high pressures and temperatures. Phys. Earth Planet. Inter. 15, 90-106. 

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