THE FEATURES OF THE REAL STRUCTURE OF K0.20NA0.78CA0.02(AL1.02SI2.98O8) FELDSPAR CRYSTAL

The X-ray diffraction studies of K0.20Na0.78Ca0.02(Al1.02Si2.98O8) cry stal are reported. The lattice constants of a triclinic unit cell are determined: a = 8.302(3) Angstrom, b = 12.950(5)Angstrom, and c = 7.08 6(2) Angstrom; alpha = 91.7(2)degrees, beta = 115.6(3)degrees, and gam ma = 90.6(3)degrees. The extinctions of X-ray reflections indicate tha t the crystal belongs to the pseudomonaclinic system, sp. gr. C-2h(3), C-2(3), or C-s(3). The Baveno twinning along (021) crystal planes was revealed. An analysis of the block structure and microstrains demonst rates that the twinning is associated the microstrain anisotropy along the [010] and [001] directions. It may be inferred that the precision refinement of the atomic structure of the crystal should be preceded by a complete characterization of its rear state.