抄録
Synthesis of a manganoan fluoromica KMg3(Si3.5Mn0.5)O10F2 with Mn in fourfold coordination was tried, utilizing mixtures of KF, MgF2, MgO, SiO2 and MnC2O4 for the starting materials. Mica crystals were obtained below 1150°C after crystallization of manganoan chondrodite (Mg, Mn)5Si2O8(OH, F)2. The X-ray structure analysis revealed that the crystal has a structure of the 1 M mica with cell dimensions of a=5.285(1), b=9.157(1), c=10.190(2)Å and β=99.97(2)°, and a chemical composition corresponding to K(Mg2.44Mn0.24)(Si3.82Mn0.18)O10F2. The structure refinement was carried out with the full-matrix least-squares procedure to the final R value of 0.043 for 1131 observed reflections. The (Si, Mn)–Oapical distance is 1.616Å and the mean (Si, Mn)–Obasal distance is 1.638Å. The mean (Si, Mn)–O distance of 1.632Å is longer than the literature value of 1.625Å for the mean Si–O distance in the SiO4 tetrahedra by 0.007Å, supporting the conclusion that Mn atoms substituted a part of Si4+ ions at the tetrahedral sites in the present experiment. The mean octahedral cation-anion distances are 2.071Å for M(1) octahedra and 2.070Å for M(2). The tetrahedral rotation angle is 1.73°, and the octahedral flattening angles are 58.4° for M(1) octahedra and 58.3° for M(2).
