Some silicate minerals such as amphiboles, biotites, cordierites and garnets were examined magnetically. Magnetic susceptibility at the room temperature of garnets is in good agreement with the theoretical value estimated by using the effective Bohr magneton number derived empirically from salts bearing above magnetic ions, while in the case of amphiboles, biotites and cordierites, which contain water in their crystal structure, magnetic susceptibility at the room temperature shows fairly larger value than expected.