Individual compounds and solid solutions are obtained under hydrothermal conditions in the Bi2O3 SiO2 MnO2 system in the form of faceted crystals and epitaxial films on the Bi24Si2O40 substrate. The crystals have the shape of a cube (for the molar ratio of the starting components Na2SiO3 center dot 9H(2)O:Mn(NO3)(2)center dot 6H(2)O > 1), a tetrahedron (for Na2SiO3 center dot 9H(2)O:Mn(NO3)(2)center dot 6H(2)O < 1), or a tetrahedron cube combination (for Na2SiO3 center dot 9H(2)O:Mn(NO3)(2)center dot 6H(2)O = 1). Crystal chemical analysis based on the data of single-crystal and powder X-ray diffraction, IR spectra, and the results of calculation of the local balance by the bond-valence method reveals formation of the Bi-24(Si4+,Mn4+)(2)O-40 phases, which probably include Mn5+ ions (epitaxial films), as well as the Bi-24(Si4+,Bi3+,Mn4+)(2)O-40 and Bi-24(Si4+, Mn4+)(2)O-40 phases in the (1-x)Bi3+ Si-24(4+) O-2(40)-x((Bi243+Mn24+O40)) system and the Bi-24(Bi3+,Mn4+)(2)O-40 phase in the (1 - x)Bi243+Bi23+(O-39 square(1)) - x(Bi243+Mn24+O40) system. Precision X-ray diffraction studies of single crystals of the Bi-24(Bi,Si,Mn)(2)O-40 general composition show that these sillenites crystallize in space group P23 and not I23 as the Bi24Si2O40 phase. The dissymmetrization of sillenite phases is observed for the first time. It is explained by a kinetic (growth) phase transition of the order disorder type due to population of a crystallographic site by atoms with different crystal chemical properties and quasi-equilibrium conditions of crystal growth in the course of a hydrothermal synthesis below 400 degrees C at unequal molar amounts of the starting components in the batch.