Synthetic celsian (barium feldspar) crystallized from a glass of nearly stoichiometric composition exhibited a diffraction pattem with very broad and almost absent diffraction peaks with l = odd indices (the basic ≈7.2-Å cell is assumed). Three models based on the random shift of layers by c/2 are proposed to explain the phenomenon: (l) twinning by the Carlsbad law, (2) coesite-like distortion, and (3) faulting in the (100) plane. A comparison of observed and calculated peak widths showed that the third model was not applicable. The trend in the change in lattice parameters was most compatible with the first model, and observed diffraction effects thus appear to be caused by random twinning faults.

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