Pressure-induced reduction of a ferric amphibole

MOST ferric salts and complexes undergo reversible reduction at high pressures^1,2. These results have important implications in geochemical studies of the mantle³ and suggest that ferric-bearing silicates might be reduced to the ferrous state at high pressures. We report here results of Mössbauer measurements at high pressures on a synthetic ferric amphibole, which is a possible component in the Upper Mantle. The data indicate that Fe³⁺ ions may be reduced to Fe²⁺ ions in minerals of the Earth's interior.