Two quadrupole splitting doublets with delta E_q = 0.74 and 1.62 mm/s were found in the montmorillonite spectra. The more intense doublet corresponds to iron in a somewhat distorted tetrahedral coordination, while the less intense corresponds to quadri-coordinated iron. The EPR spectrum also exhibits two lines with a q-factor of 3 and 4.3, which corresponds to transformed minerals.

Supplement to: Grechishkin, V S; Zangalis, K P; Murin, I V; Emelyanov, Emelyan M; Sivkov, Vadim P; Kharin, Gennady S (1979): Nuclear gamma resonance and electronic paramagnetic resonance spectra of minerals of the glauconite and montmorillonite groups. Oceanology, 19(3), 290-293