Solid solutions olivine

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

Bostrom D. (1987). Single-crystal X-ray diffraction studies of synthetic Ni-Mg olivine solid solutions. Amer. Mineral, 66 770-776. 

Bostrom D. (1988). Experimental studies of (Ni,Mg)—and (Co,Mg)—olivine solid solutions by single crystal X-ray diffraction and solid state emf method. Ph.D. thesis. Department of Inorganic Chemistry, University of Umea, Umea, Sweden. 

Matsui Y. and Syono Y. (1968). Unit cell dimension of some synthetic olivine group solid solutions. Geochem. Jour, 2 51-59. 

Ottonello G. and Morlotti R. (1987). Thermodynamics of nickel-magnesium olivine solid solution. J. Chem. Thermodyn., 19 809, 818. 

Seifert S. and O Neill H.St. C. (1987). Experimental determination of activity-composition relations in Ni2Si04-Mg2Si04 and Co2Si04-Mg2Si04 olivine solid solutions at 1200 K and 0.1 MPa and 1573 K and 0.5 GPa. Geochim. Cosmochim. Acta, 51 97-104. 

For inter diffusion between same-valence ions (ionic exchange) in an aqueous solution, or a melt, or a solid solution such as olivine (Fe +, Mg +)2Si04, an equation similar to Equation 3-135c has been derived from the Nemst-Planck equations first by Helfferich and Plesset (1958) and then with refinement by Barter et al. (1963) with the assumption that (i) the matrix (or solvent) concentration does not vary and (ii) cross-coefficient Lab (phenomenological coefficient in Equation 3-96a) is negligible, which is similar to the activity-based effective binary diffusion treatment. The equation takes the following form ... 

Diffusion in the crystai. If a crystal has a fixed composition, such as quartz, there is no need to consider diffusion in the crystal except for isotopic exchange. For a crystal that is a solid solution, such as olivine, the equilibrium composition at the crystal surface may be different from the initial composition. There would be diffusion in the crystal. Although this problem has not been investigated before in the literature, it is not a difficult problem and it can be solved using the same steps as diffusion in the melt. The diffusion equation is... 

Example 4.1. Suppose olivine and garnet are in contact and olivine is on the left-hand side (x<0). Ignore the anisotropic diffusion effect in olivine. Suppose Fe-Mg interdiffusion between the two minerals may be treated as one dimensional. Assume olivine is a binary solid solution between fayalite and forsterite, and garnet is a binary solid solution between almandine and pyrope. Hence, Cpe + CMg= 1 for both phases, where C is mole fraction. Let initial Fe/(Fe- -Mg) = 0.12 in olivine and 0.2 in garnet. Let Xq = (Fe/Mg)gt/ (Fe/Mg)oi = 3, >Fe-Mg,oi = 10 ° mm+s, and Dpe-Mg,gt =... 

Forstente. Pure forsterite is rare in nature. Most natural magnesium orthosilicates form solid solutions of fayalite, Fe2Si04, and forsterite. Forsterite refractories are usually made by calcining magnesium silicate rock such as dunite, serpentine, or olivine with sufficient magnesia added to convert all excess silica to forsterite and all sesquioxides to magnesia spinels. 

Olivine - solid solution of Mg2Si04 (forsterite) and Fe2Si04 (fayalite). 

Olivine and other orthosilicates have been exposed to oxygen potential gradients in order to investigate the demixing of solid solutions and internal reactions (oxidation, decomposition). The corresponding formalism was outlined in Chapters 8 and... 

Solid solution A group of minerals or other compounds with the same crystalline structure and whose chemical compositions vary somewhat due to substitutions between two or more different elements or pairs of elements. As examples, Mg2+ and Fe2+ substitute for each other to form a solid solution in olivine ((Fe,Mg)2SiC>4) and (CaAl)5+ and (NaSi)5+ substitute for each other in plagioclase. 

Other examples discussed later where changes of spectrum profiles across a solid-solution series correlate with cation ordering in the crystal structure include Ni-Mg olivines (Hu et al., 1990), in which Ni2+ ions are strongly ordered in the Ml sites ( 5.4.2.4), and Mg-Fe2+ orthopyroxenes mentioned earlier where strong enrichment of Fe2+ ions occurs in the very distorted M2 sites ( 5.5.4). 

Therefore, according to this calculation, there is an excess CFSE (enthalpy) of mixing of about -1.6 kJ/(mole of olivine). Similarly, the formation of all intermediate olivines by mixing of Mg2Si04 and Fe2Si04 components results in an excess CFSE of mixing. This is illustrated in fig. 7.3. These results imply that there is a heat of mixing term and that the olivine series is not an ideal solid-solution of forsterite and fayalite. 

Obata, M., Banno, S. Mori, T. (1974) The iron-magnesium partitioning between naturally occurring coexisting olivine and Ca-rich clinopyroxene an application of the simple mixture model to olivine solid solution. Bull. Soc. Franc. Mineral., 97,101-7. 

Major silicates Olivine solid solution forsterite fayalite Orthopyroxene solid solution enstatite ferrosilite Clinopyroxene solid solution diopside hedenbergite Pigeonite Augite... 

Fig. 5.10. Calculations of the properties of olivine solid solutions (see Ottonello, 1987, for full details and data sources) (a) Calculated phase field boundaries in the system (Mn,Mg),Si04 full circles are calculated boundaries, dashed curves are extrapolated, dotted lines are experimental solubility gap. (b) Plot of site occupancy versus molar composition along the binary join (Ni,Mg)2Si04-...

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. 

Val ter, A.A., 1969. On the distribution of magnesium and iron between coexisting olivine and orthopyroxene solid solutions with high iron content. Dokl. Akad. Nauk S.S.S.R. (Rep. Acad. Sci, U.S.S.R.), 187(2) 410-413 (in Russian). 

Nagahara H., Kushiro I., Mysen B., and Mori H. (1988) Experimental vaporization and condensation of olivine solid solution. Nature 331, 516-518. 

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