Refinement of the crystal structure of sanidine-like feldspar

The crystal structure of sanidine-like feldspar of the composition KAlSi3O8 from the Khibiny alkaline massif (the Kola Peninsula) has been refined (X- ray diffraction analysis; automated Syntex P (1) over bar diffractometer; 2 theta : theta scanning technique; 2320 reflections; R-(hkl) = 0.0409; anis otropic refinement; AREN program package). The data obtained for KAlSi3O8 a re: a = 8.615(9), b = 13.030(7), c = 7.200(5) Angstrom, alpha = 89.99(5)deg rees, beta = 116.01(6)degrees, gamma = 89.98(7)degrees, Z = 4, sp. gr. C (1 ) over bar. Microtwinning revealed in the crystal structure of the mineral explains the simultaneous existence of two structural-optical types in one sample-"high" and "low" sanidines. (C) 2000 MAIK "Nauka/Interperiodica".