Fayalite

The SSI (solid-state imaging) camera on board the Galileo spacecraft transmitted impressive high-resolution pictures of Io s volcanic activity. Active lava lakes, lava curtains , calderas, mountains and plateaus can be seen (McEwen et al., 2000). The Hubble telescope detected both S2 gas and SO2 in a SO2 to S2 ratio of 1 4 in the smoke trail of the volcano Pele. This value suggests an equilibrium between silicate magmas in the neighbourhood of the quartz-fayalite-magnetite buffer (see Sect. 7.2.2). 

At greater depths, the redox characteristics are mainly determined by another mineral system fayalite (Fe2Si04), magnetite and quartz (Si02) (theFMQ system). The buffer properties of the two systems can be expressed in terms of the following equations ... 

First attempts to incorporate pre-formed magnetite colloids within alginate/silica nanocomposites via a spray-drying process have been described, but formation of lepidocrocite y-FeOOH and fayalite Fe2Si04 was observed, attributed to Fe2+ release during the aerosol thermal treatment [53],... 

A2Si04-B2Si04 Olivine Mg2Si04-Fe2Si04, end members forsterite and fayalite, sobd solution is olivine... 

Olivine is assumed to be the only mineral precipitating and the fa and fo subscripts refer to pure fayalite and forsterite. Upon crystallization of the incremental amount dM i of cumulate, the incremental amount dMfa of fayalite is precipitated, and, since the iron content of fayalite is constant... 

CfaFe° and CfoMg0 being the contents of FeO in fayalite and MgO in forsterite, the... 

Similarly to Mn(IV)- and Fe(III)-oxides, some primary minerals were shown to promote polymerization of hydroquinone (19). Olivines, pyroxenes, and amphiboles accelerated the polymerization reaction to a greater extent than micas and feldspars. Microcline and quartz were ineffective- The effect was greatest for tephroite, a manganese-bearing silicate with the ideal chemical formula M SiO. Fayalite, the corresponding Fe(II) analog (Fe2Si0 ), was effective, but to a lesser extent. 

Olivine is the principal mineral (in terms of mass) of the earth s upper mantle where it is present as a combination of the two main components forsterite (85-95 mol.%) and fayalite (5-15 mol.%). In the earth mantle the increase in seismic velocity with depth is believed to be due to the presence of denser modifications of common minerals. 

Fayalite (melting point 1205°C) and forsterite (melting point 1890°C) form continuous solid solutions (the melting diagram of their binary mixtures correspond to the type exemplified in Fig. 2.28). Phase equilibria as a function of pressure, show, however, transition into the spinel structure. (cF56-MgAl204, spinel structural type). 

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. 

Olivine Name Forsterite Chrysolite Hyalosiderite Hortonolite F err o-hortonolite Fayalite... 

Present M sbauer Studies of Natural Pyroxenes and Olivines. Table IX gives the major element chemical compositions of the silicate minerals examined in this study. Table X compares the Mossbauer parameters of these minerals, while Figures 9-13 show representative Mossbauer spectra. Fayalite (Figure 9) is the only olivine in this group. The two lines are, however, somewhat broadened (0.35 and 0.39 mm./ sec.) compared with the width of natural iron foil lines observed with our source (0.24 mm./sec.) and suggest the near coincidence of two quadrupole-split doublets resulting from Mi and M2 sites. Analysis of this "two-line spectrum into a four-line spectrum in the manner described by Evans et al (11) could possibly yield parameters for the two iron sites, but this was not undertaken since both lines appear symmetric. The "two-line quadrupole splitting of 2.78 mm./sec. is somewhat smaller... 

Table XIII. Mossbauer Parameters for a Synthetic Fayalite-Fosterite (Fa-Fo) Series as a Function of Iron Concentration Expressed...

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