Determination of crystal structure of omphacite

<正> The chemical formula of omphacite was expressed with （MⅡMⅠ）(Si, AI)2O6.Cations that occupied the MⅡ site were large cations such as Ca or Na, and Na/（Na+Ca） ratio ranged from 0.2 to 0.8; the 6-coordinated MⅠ site accommodated cations such as Mg, Fe2+,Al, Fe3+ ,and Al/（Al+Fe3+） ratio was more than 0.5 Omphacite space groups reported were C2/c, P2, P2/n, P2/c, cell parameters are a0 = 0.9600—0.9630 nm, b0 = 0.8750—0.8830 nm, C0 =0.5230—0.5290 nm,β = 106°40'—107°10'. The sample was picked up from the eclogites in Zhucheng County, Shangdong Province. The intensity data were collected with the RIGAKU RASA Ⅱ -S four-circle single crystal diffractometer. The correct structure model was obtained by using the Patterson method and Fourier synthesis, SHELX-76 program, structure refinement with 905 independent diffraction points （|F0|> 3σ|F0 |）. After the structure parameter refinement, the R-factor reduced to 0.0515. The crystal structure analysis indicates that omphacite has a new s