Enstatite-ferrosilite series

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. 

Fig. 3.26 RT Mossbauer spectra of synthetic samples of the enstatite-ferrosilite series showing a gradual increase of Fe " on Ml sites (from Dyar et al. [209])...

Table XI. Mossbauer Parameters of a Synthetic Enstatite-Ferrosilite ( n-Fs) Series as a Function of Iron Concentration Expressed as Percent Ferrosilite Present by Subscript on Fs...

The activity of the FeSiOj component of the MgSiOj-FeSiOj (enstatite-ferrosilite) solid solution was obtained by using as experimental charges compositions in this series plus silica plus Fe metal, in the furnace atmosphere having the controlled /o as described above. The relevant reaction is... 

Orthopyroxenes have compositions close to the enstatite-ferrosilite MgSi20g-FeSi206 tie line. The spectra consist of two ferrous doublets, which can be clearly resolved (Fig. 3.25). The one with the small quadrupole splitting (see Table 3.16) can be assigned to the distorted M2 sites [208]. In the (Mg,Fe)Si20e series this doublet remains rather intense evoking the preference of iron for the M2 sites. [209]. 

Mossbauer spectra have been measured for various tektites, as well as for both natural and synthetic iron-bearing silicate minerals. These results are reported and compared with other similar studies available in the literature. The ratios of the intensities of the appropriate Mossbauer lines have been used to determine the ferric-ferrous ratios where possible. The spectra of the ferrosilite-enstatite series of pyroxenes show four lines which are interpreted as two quadrupole split doublets, and the ratio of the intensities of these lines indicates the degree of ordering in filling the available metal ion sites. Similar studies on the fayalite-forsterite series of olivines are also reported. 

Mossbauer spectrum of ferrosilite-enstatite series of pyroxenes... 

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