The Crystal Structure of the Dioctahedral Mica 2m2 Determined by High Voltage Electron Diffraction

The structure of a dioctahedral 2M2 mica was defined by high voltage electron diffraction. The cell parameters are: a = 8-965, b ~ 5-175, c = 20.31 A, fl = 100 ~ 40', Z = 4, space group C2/c. Despite the peculiar character of the layer dispogition (or 4 as ~r~ as) , the oxygens of the layers are packed according to the cubic law. Consequently, the interlayer cations K have a trigonal prismatic coordination. The angle of tetrahedral twist is 11 ~ 20'. The interatomic distances T-O indicate ordered replacements of AI for Si.