Observation of free electron cyclotron resonance in NaAlSi3O8 feldspar: Direct determination of the effective electron mass

We report the first observation of cyclotron resonances in alkali feldspars, using highly sensitive optical detection methods. In Na-feldspar (NaAlSi3O8). a near isotropic effective electron mass value of m(c)(*) = 0.79m, has been determined. The significance of this measurement in terms of the optical transition energies of shallow donor centres is considered.</p