By refining the atomic scattering power of each of the four cation sites, M1 through M4, of the crystal structure of Cummingtonite, the distribution of Mg2+ and Fe2+ over these sites were determined to be:
M1:84% Mg and 16% Fe,
M2:95% Mg and 5% Fe,
M3:84% Mg and 16% Fe,
M4:13% Mg and 87% Fe.
Ghose's original data (1961) were used for this work. The results demonstrate the usefulness of the f-refinement technique for the evaluation of mixed populations for more than one equipoint.