Metavivianite and kerchenite " a review

ABSTRACT. Metavivianite has been shown to be not dimorphous with vivianite. Assuming the homogeneity and uniformity of the original type samples, it is a triclinic hydrated ferri-ferrous hydroxy phosphate whose formula may be given as Fe~+xFe3+(po4)2(OH)x(8--x)H20 where x> 1.4. The precise oxidation limits between which the triclinic lattice is stable are not known but the structure persists close to total oxidation of all iron. The structure of metavivianite was established using a frag-ment of kerchenite whose formula s originally given is covered by the general metavivianite formula. Assuming the homogeneity of the original (1907) samples, kerchenite and metavivianite appear to be identical