The three-dimensionally modulated incommensurate crystal structure of lazurite from the Baikal region was determined for the first time. The structure was solved within the cubic system with the unit-cell parameter a(cub) = 9.077(1) Angstrom and the (3+2)-dimensional superspace group Pnn2(q(1), q(2)) under the assumption of a twin model consisting of three orthorhombic components related by a threefold axis along the [111] direction. The structure was refined using 257 main reflections and 2392 first-order satellite reflections with the isotropic thermal parameters to wR(0) = 1.98% and wR(1) = 7.50% respectively. (C) 2003 MAIK "Nauka/Interperiodica".