Electron paramagnetic resonance of Fe3+ in forsterite (Mg2SiO4)

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Abstract
The electron paramagnetic resonance of Fe3+ in synthetic forsterite (Mg2SiO4) has been observed at 35 GHz and 9 GHz. The spectrum is interpreted in terms of a spin Hamiltonian of orthorhombic symmetry having the crystal C plane as mirror plane with two equivalent sites related by the b or a reflection planes. Hence, the Fe3+ ions are ordered in the M(2) sites of the structure. Neither the valence state nor the site occupancy of Fe3+ is altered by heat treatments up to 1100°C. The valence state is altered by irradiation at room temperature. This alteration is reversed by heating to 350°C in air. The formation of a broad EPR absorption during heat treatment between 600 and 800°C is attributed to the oxidation and precipitation of Fe2+.