High-Order Supersatellite Reflections in Labradorite. A SynchrotronX-ray Diffraction Study

The supersatellite reflections in the feldspar mineral labradorite are related to the Bøggild intergrowth, a lamellar structure with a periodicity of about 1500 Å. With high-resolution X-ray diffraction using synchrotron radiation, supersatellites up to fourth order are observed. The system is an example for a natural superstructure with high-order diffraction harmonics. The satellite intensities reflect a transverse displacement modulation with a large amplitude. The complete unit cell of labradorite is affected by the displacement. In this context, various possible displacement functions are discussed. A Fourier expansion of the displacement function that yields the best agreement between measurement and theory has nearly triangular shape. The line width of the satellites characterizes imperfections of the lamellar superstructure: It increases linearly with satellite order, which is ascribed to uncorrelated variations (FWHM = 480 Å) of the lamellar thickness.