STUDY OF THE Fe3+/Fe2+ RATIO IN NATURAL CHROMITES (Fex, Mg1-x) (Cr1-y-z, Fey, Alz)O4 G. A. FATSEAS, J. L. DORMANN and H. BLANCHARD J. Phys. Colloques, 37 C6 (1976) C6-787-C6-792 DOI: 10.1051/jphyscol:19766166