Prepn from CoCl2 and (NH4)2HPO4: Klement, Haselbeck, Z. Anorg. Allg. Chem. 334, 27 (1964); from Ca(H2PO4)2: Vickery, US 2914380 (1959 to Horizons). Review: de Bie, Doyen, Cobalt 15, 3-13; 16, 3-15 (1962). See also Colour Index vol. 4 (3rd ed., 1971) p 4665.