Citation: Oberti, R.; Hawthorne, F. C.; Camara, F.; Raudsepp, M. (1999). Unusual M3+ cations in synthetic amphiboles with nominal fluoro-eckermannite composition: Deviations from stoichiometry and structural effects of the cummingtonite component Sample: Cr2, Na1.00Na1.75Mg.25Mg4.25Cr.75Si8O22F2. American Mineralogist, 84, pp. 102-111.