Room temperature 57Fe Mössbauer spectra have been recorded for six hornblendes and seven biotites from the Sierra Nevada Batholith, California. The hornblende spectra have been resolved into three Fe2+ doublets due to Fe 2+ in M1, M2, and M3; and one Fe3+ doublet due to Fe3+ mainly in M2. The biotite spectra have been resolved into two Fe2+and two Fe3+ doublets due to Fe2+ and Fe3+ in both Ml and M2. Using the areas of the peaks, Fe3+/Fe2+ ratios have been derived. For biotites, these are found to be in good agreement with the chemical analysis values; for hornblendes, the constant relating the chemical and Mössbauer Fe3+ /Fe2+ values is 1.13 ± 0.02. The accuracy of the non-destructive Fe3+/Fe2+ analysis is within 2 to 4 percent for most samples. Saturation corrections for such analyses are shown to be negligible

The ferrous site populations show that Fe2+ orders in the Ml and M3 positions in hornblendes. There is a small amount of ferrous ordering on M2 in biotites, which increases as the ferrous content decreases.

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