Fayalite crystal structure

Princivalle, F. Secco, L. (1985) Crystal structure refinement of 13 olivines in the forsterite-fayalite series from volcanic rocks and ultramafic nodules. Tschermaks Mineral Petrol. Mitt., 34,105-15. 

Another way that the choice of formulas can differ is that some choices can be multiples of other choices. This is most often seen in choosing solute species in solids, because there are no real species, just a crystal structure that is a solid solution. For example, the mineral oUvine is a soUd solution of two components, forsterite (Mg2Si04) and fayalite (Fe2Si04). The solution is represented by (Mg, Fe)2Si04, because the Mg and Fe atoms share the same positions in the crystal structure. 

For the pseudo-tetragonally elongated Ml octahedral site in the olivine structure, an alternative method for obtaining the CFSE of Fe2+ ions in this site is to evaluate the ligand field splitting parameters in the equatorial plane and along the axial direction using eqs (3.14) to (3.16). The crystal field spectral data for the fayalite Ml site (see fig. 5.11a) yield values for 10 Dq(m) and 10 Dq(eq) of 8,172 cm-1 and 9,327 cm-1, respectively. The mean 10 Dq value of 8,942 cm-1 and the CFSE of 4,133 cm-1 compare favourably with A0 = 8,830 cm-1 and CFSE = 4,250 cm-1 for Fe2+ in the fayalite Ml sites determined by the baricentric method (fig. 5.11a). 

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