Fayalite



Fayalite

General
CategoryMineral
silicate (Fe2SiO4)
Identification
ColorPale yellow, amber and green
Orthorhombic
Cleavage{010} moderate, {100} weak
FractureConchoidal
Mohs Scale hardness6.5
LusterVitreous
Refractive indexα = 1.827,
β = 1.869,
γ = 1.879
Specific gravity4.392


Fayalite (Fe2SiO4) is the space group Pbnm) with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.

Iron rich olivine is a relatively common constituent of acidic and alkaline amphiboles. It also occurs in medium-grade thermally metamorphosed iron-rich sediments.

Fayalite is stable with quartz at low pressures, whereas more magnesian olivine is not, because of the reaction olivine + orthopyroxene. Iron stabilizes the olivine + quartz pair. The pressure and compositional dependence of the reaction can be used to calculate constraints on pressures at which assemblages of olivine + quartz formed.

Fayalite can also react with fugacity of oxygen in laboratory experiments. It can also be used to calculate the fugacity of oxygen recorded by mineral assemblages in metamorphic and igneous processes.

References

  • Deer, W. A., Howie, R. A., and Zussman, J. (1992). An introduction to the rock-forming minerals (2nd ed.). Harlow: Longman ISBN 0-582-30094-0
 
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