Infrared reflectance spectra of fayalite, and absorption data from assorted olivines, including pressure and isotope effects

Polarized single-crystal infrared (IR) reflectance spectra measured for synthetic fayalite (Fe2SiO4) possess all but one of the peaks mandated by symmetry plus a few weak bands attributable to overtones. Fayalite has a band at 86 cm(-1), which is below the frequency range commonly examined, suggesting that vibrational spectra of ferrous minerals may need remeasuring. B-2u polarizations were also measured for natural monticellite (nearly MgCaSiO4) and synthetic (Mg2SiO4)-O-18. Thin film absorption data were collected for the above spe cies, Co2SiO4, Mn2SiO4, Mg2SiO4, (Mg1.9Fe0.1)SiO4, Mg2GeO4 and Mn2GeO4. The relationships of IR peak positions (from these data and from previous single-crystal studies) with the inverse square root of the average cation mass were used to make band assignments, to estimate the positions for missing bands, and to determine which peaks are degenerate. The pressure dependencies of monticellite IR peaks were measured and resemble those of other olivines.