Journal article

On the symmetry of optically isotropic modulated lazurites from the Baikal region

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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