The crystal structure of taeniolite, KLiMg2Si4O10F2

Abstract

Abstract Taeniolite, KLiMg2Si4O10F2, was synthesized from a mixture of KF, LiF, MgO and SiO2, and the crystal structure was refined with three-dimensional x-ray diffraction data. The crystals are monoclinic (1 M type) with the space group C2/m, a = 5.231(1), b = 9.065(2), c = 10.140(1) Å, β = 99.86(2)°, and Z = 2. Refinements with the full-matrix least-squares procedure gave the final R value of 0.024 for 1303 observed reflections. All the bridging Si–O distances are 1.638(1) Å, whereas the nonbridging one is 1.586(1) Å. A comparison of several 1 M-type micas clearly indicates the effect of octahedral cations on the distortion of (Si,Al)O4 tetrahedra. Li+ ions are more concentrated at the M(2) site than at M(1) in conformity with the size difference between the coordination octahedra. The ditrigonal distortion of the tetrahedral sheets is still smaller than that of KMg2.5Si4O10F2, having the tetrahedral rotation angle α of 1.08°. The octahedral flattening angles, ψ are 57.8° and 57.9° for M(1) and M(2) sites, respectively.