Koenenite
Diffraction data computed using the structure from the paper listed below, 
along with the cell parameters refined from single crystal data of 060989
      Allmann R, Lohse H N, Hellner E
      Zeitschrift fur Kristallographie 126 (1968) 7-22
      Die kristallstruktur des koenenits, eine doppelschichtstruktur mit zwei
      inkommensurablen teilgittern
      Note: one of two substructures in koenenite

      CELL PARAMETERS:   4.1100  4.1100 32.9000   90.000   90.000  120.000
      SPACE GROUP: R-3m      

           ATOM        X         Y         Z     OCCUPANCY  ISO(B)
            Na     0.00000   0.00000   0.00000     0.667     2.300
            Ca     0.00000   0.00000   0.00000     0.222     2.300
            Mg     0.00000   0.00000   0.00000     0.111     2.300
            Cl     0.66667   0.33333   0.04636     1.000     3.600

            X-RAY WAVELENGTH:     1.541838
            BOUNDS ON TWO THETA:    0.0  90.0
            LIMITS IMPOSED ON THE INDICES ARE:  +/-  3 +/-  3 +/- 30
            MAX. ABS. INTENSITY / VOLUME**2:      35.51783454    
            The INTENSITY cut off value is   1.00

               2-THETA      INTENSITY    D-SPACING   H   K   L
                 8.06        100.00       10.9667    0   0   3
                24.35          1.42        3.6556    0   0   9
                25.61          4.03        3.4789    0   1   2
                27.30         13.35        3.2666    1   0   4
                28.51          3.05        3.1307    0   1   5
                31.53         16.49        2.8375    1   0   7
                37.22          5.62        2.4160    1   0  10
                39.35          3.58        2.2898    0   1  11
                44.07          4.88        2.0550    1   1   0
                44.87          5.14        2.0198    1   1   3
                46.30          3.96        1.9611    0   1  14
                52.62          1.23        1.7394    0   2   4
                53.93          1.38        1.7002    0   1  17
                55.19          1.89        1.6644    0   2   7
                73.18          1.04        1.2934    2   1   7
================================================================================
       XPOW Copyright 1993 Bob Downs, Ranjini Swaminathan and Kurt Bartelmehs
  For reference, see Downs et al. (1993) American Mineralogist 78, 1104-1107.