Refinement of crystal structure of mangan-neptunite, the manganese analogue of neptunitc, was carried out in the two space groups (Cc and C2/c). The mineral is monoclinic, the correct space group Cc; its unit cell parameters: a = 16.4821 (6), b = 12.5195(4), с = 10.0292 (3) A, p = 115.474( 1)°, V = 1868.31 A3. The crystal structure was refined to Д, = 0.0307 (wR2 = 0.0901) on the base of 4892 observed reflections with \Fhkl\ > 4o|fM;|. The most suitable model is acentric one, that is connected with the Ti- and (Fc, Mn, Mg)-ordering in the structure. Ti-octahcdra are strongly distorted and consist of one short bond Ti-О (1.7 A), one long bond (2.2 A) and four equal bonds (2.0 A). Fc-octahcdrons have regular shape, with all Fc-О bonds approximately equal.
