Cs-ferriannite as a possible host for waste cesium; crystal structure and synthesis

Cs-ferriannite, ideally CsFe (super 2+) (sub 3 ) (Fe (super 3+) Si (sub 3) )O (sub 10) (OH) (sub 2) , was synthesized as euhedral crystals, starting from an oxide mix, at 550 degrees C and 0.1 GPa PH (sub 2) O. The crystal structure of its 1M polytype was refined in the C2/m space group to R 5.5%. All octahedral positions as well as 23% of tetrahedral positions are occupied by iron. The octahedral sheet is geometrically homo-octahedral with all octahedra the same size; the tetrahedral and octahedral sheets are virtually undistored. Cs-ferriannite is the 1M mica with the largest unit cell known to date: a 5.487, b 9.506, c 10.826 Aa, beta 99.83 degrees , Z = 2. This mica appears to be a stable crystalline phase that may serve for fixation and storage of radioactive Cs isotopes in its interlayer.