Initial Publication Date: July 14, 2005


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  1. What is the coordination numbers of Si, Al, and K in the sanidine structure?
  2. What ions are in tetrahedral coordination in this structure? (Look carefully!) How are the tetrahedra connected to each other
  3. Look down the b-axis and rotate the model around this axis. Do the atomic positions exactly repeat themselves after 90°, 120°, or 180° rotations? (Hint: look down the center of the "channels" as seen in this orientation.)
  4. All of the tetrahedral sites are essentially the same in this model. What would happen to the symmetry if the structure was "ordered" such that every fourth tetrahedron was somehow unique (e.g., in its size or shape): would it increase or decrease?