Refined crystal structure of iron-rich triclinic astrophyllite

Crystal structure of Fe-rich triclinic astrophyllite K2NaFe7[Ti2Si8O26F](OH )(4) is refined (a Syntex P (1) over bar automatic diffractometer, 3809 ref lections, 2 theta/theta scan, R = 0.041): a = 5.365(2), b = 11.88(1), c = 2 1.03(2) Angstrom, alpha = 84.87(6)degrees, beta = 92.25(5)degrees, gamma = 103.01(4)degrees, sp, gr. A (1) over bar, Z = 2, d(calcd) = 3.29 g/cm(3). T he refined structure is identical to that reported earlier. The structure i s built by three-layer TOT sheets in which an O layer of Fe-octahedra is sa ndwiched between the T layers consisting of Si-tetrahedra and Ti-octahedra. It is established that differently chosen unit cells of the mineral are in terrelated. (C) 2000 MAIK "Nauka/Interperiodica".