Cryolite
      Yang H, Ghose S, Hatch D M
      Physics and Chemistry of Minerals 19 (1993) 528-544
      Ferroelastic phase transition in cryolite, Na3AlF6, a mixed
      fluoride perovskite: high temperature single crystal X-ray
      diffraction study and symmetry analysis of the transition mechanism
      Sample: T = 900 K
      _database_code_amcsd 0007750

      CELL PARAMETERS:    5.6333   5.6273   7.9619   90.000   90.000   90.000
      SPACE GROUP: Immm      
      X-RAY WAVELENGTH:     1.541838
      Cell Volume:    252.394
      Density (g/cm3):      2.762
      MAX. ABS. INTENSITY / VOLUME**2:      4.259513451    
      RIR:      0.502
      RIR based on corundum from Acta Crystallographica A38 (1982) 733-739
               2-THETA      INTENSITY    D-SPACING   H   K   L   Multiplicity
                19.30         17.80        4.5986    1   0   1         4
                19.32         33.81        4.5954    0   1   1         4
                22.33         59.86        3.9812    1   1   0         4
                22.33         24.62        3.9810    0   0   2         2
                31.77         29.17        2.8166    2   0   0         2
                31.79        100.00        2.8151    1   1   2         8
                31.80         31.29        2.8136    0   2   0         2
                39.18          3.30        2.2993    2   0   2         4
                39.21          2.82        2.2977    0   2   2         4
                45.57         28.57        1.9906    2   2   0         4
                45.57         13.81        1.9905    0   0   4         2
                51.29          1.45        1.7812    3   1   0         4
                51.32          1.89        1.7804    2   2   2         8
                51.32          2.59        1.7804    1   1   4         8
                51.34          1.44        1.7797    1   3   0         4
                56.61          6.43        1.6259    3   1   2         8
                56.62          3.58        1.6255    2   0   4         4
                56.64          3.63        1.6250    0   2   4         4
                56.65          6.41        1.6247    1   3   2         8
                66.42          3.04        1.4075    2   2   4         8
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       XPOW Copyright 1993 Bob Downs, Ranjini Swaminathan and Kurt Bartelmehs
  For reference, see Downs et al. (1993) American Mineralogist 78, 1104-1107.