Abstract

The incommensurately modulated twinned crystal structure of lazurite from the Baikal region is presented for the first time. The orthorhombic structure was solved in a pseudo cubic unit cell, a(cub) = 9.077(1) Angstrom, and in the (3 + 2)D superspace group Pnn2(alphaalpha0, alpha - alpha0). The crystal is twinned with three components oriented along the [111] axis. In order to include all the measured satellites, the structure was also refined with trigonal symmetry R3, where the average structure refined to R = 3.6%. A 3D-modulated twinned trigonal structure will be further considered.

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