Iowaite
Diffraction data computed using the structure from the paper listed below, 
along with the cell parameters refined from the powder pattern of R060272
      Allmann R, Donnay J D H
      American Mineralogist 54 (1969) 296-299
      About the structure of iowaite

      CELL PARAMETERS:   3.1104  3.1104 23.5100   90.000   90.000  120.000
      SPACE GROUP: R-3m      

           ATOM        X         Y         Z     OCCUPANCY  ISO(B)
            Mg     0.00000   0.00000   0.00000     0.800     0.800
            Fe     0.00000   0.00000   0.00000     0.200     0.700
            OH     0.00000   0.00000   0.37600     1.000     1.000
            OH     0.00000   0.00000   0.50000     0.600     1.000
            Cl     0.00000   0.00000   0.50000     0.200     1.000

            X-RAY WAVELENGTH:     1.541838
            BOUNDS ON TWO THETA:    0.0  90.0
            LIMITS IMPOSED ON THE INDICES ARE:  +/-  2 +/-  2 +/- 21
            MAX. ABS. INTENSITY / VOLUME**2:      26.46199753    
            The INTENSITY cut off value is   1.00

               2-THETA      INTENSITY    D-SPACING   H   K   L
                11.29        100.00        7.8367    0   0   3
                22.69         29.75        3.9183    0   0   6
                34.15         30.05        2.6256    0   1   2
                36.70          2.68        2.4488    1   0   4
                38.52         13.07        2.3373    0   1   5
                45.69         30.52        1.9857    0   1   8
                51.60          8.11        1.7713    1   0  10
                54.83          3.46        1.6743    0   1  11
                59.43         11.07        1.5552    1   1   0
                60.71          4.98        1.5255    1   1   3
                61.79          2.56        1.5015    1   0  13
                64.46          6.31        1.4455    1   1   6
                65.50          2.80        1.4250    0   1  14
                70.36          2.40        1.3381    2   0   2
                73.08          1.27        1.2948    2   0   5
                73.40          4.73        1.2899    1   0  16
                78.05          3.75        1.2244    2   0   8
                82.55          1.43        1.1687    0   2  10
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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.