On Magnetic Susceptibility of Olivines

The magnetic susceptibility of several olivines, xFe2SiO4⋅(1-x)Mg2SiO4 with varying x has been measured. The results showed that the olivines are paramagnetic and that their molecular magnetic susceptibility χmol can be expressed empirically by χmol=2x× 10-2emn/mol at the room temperature. Using the accepted values of the Bohr magneton number of Fe+2 ion, and assuming that the Fe+2 ions are embedded isolatedly in the crystal, the paramagnetic susceptibility of olivines at the room temperature can be calculated as χmol=2.2x∼2.6x×10-2emn/mol, provided that the other constituents such as Mg+2 and SiO4 are only diamagnetic. The comparison of the empirical and the calculated values seems to justify the above simple calculation. We expect such calculation will also valid for other rock-forming paramagnetic minerals.