Huntite
Diffraction data computed using the structure from the paper listed below, 
along with the cell parameters refined from the powder pattern of R040126
      Dollase W A, Reeder R J
      American Mineralogist 71 (1986) 163-166
      Crystal structure refinement of huntite, CaMg3(CO3)4, with X-ray powder data

      CELL PARAMETERS:   9.5027  9.5027  7.8212   90.000   90.000  120.000
      SPACE GROUP: R32       

           ATOM        X         Y         Z     OCCUPANCY  ISO(B)
            Ca     0.00000   0.00000   0.00000     1.000     0.940
            Mg     0.54430   0.00000   0.00000     1.000     0.940
            C      0.00000   0.00000   0.50000     1.000     0.940
            C      0.45350   0.00000   0.50000     1.000     0.940
            O      0.86630   0.00000   0.50000     1.000     0.940
            O      0.58950   0.00000   0.50000     1.000     0.940
            O      0.45690   0.13550   0.51610     1.000     0.940

            X-RAY WAVELENGTH:     1.541838
            BOUNDS ON TWO THETA:    5.0  90.0
            LIMITS IMPOSED ON THE INDICES ARE:  +/-  7 +/-  7 +/-  7
            MAX. ABS. INTENSITY / VOLUME**2:      17.40591402    
            The INTENSITY cut off value is   1.00

               2-THETA      INTENSITY    D-SPACING   H   K   L
                15.63          1.40        5.6693    1   0   1
                24.44          1.99        3.6416    0   2   1
                30.94         18.79        2.8903    2   1   1
                31.56        100.00        2.8346    2   0   2
                32.64          2.36        2.7432    3   0   0
                34.40          8.81        2.6071    0   0   3
                36.93          9.24        2.4343    1   2   2
                37.87         10.46        2.3757    2   2   0
                39.42          5.53        2.2856    1   1   3
                41.20          7.52        2.1911    1   3   1
                45.59          7.64        1.9897    4   0   1
                46.04         23.47        1.9713    3   1   2
                49.68          3.47        1.8353    3   2   1
                50.10          2.51        1.8208    0   4   2
                50.84          3.35        1.7958    4   1   0
                51.76         15.70        1.7660    0   2   4
                52.08         14.64        1.7560    2   2   3
                53.93          3.19        1.7002    2   3   2
                58.26          9.65        1.5838    3   3   0
                60.72          2.65        1.5254    2   4   1
                62.55          5.29        1.4849    1   3   4
                62.83          2.13        1.4789    1   4   3
                62.83          2.74        1.4789    4   1   3
                64.12          2.84        1.4524    5   1   1
                64.48          2.81        1.4452    4   2   2
                65.90          1.91        1.4173    4   0   4
                66.96          2.47        1.3975    1   2   5
                67.78          1.19        1.3826    1   5   2
                68.40          2.46        1.3716    6   0   0
                69.44          1.59        1.3536    3   3   3
                71.61          2.96        1.3178    5   2   0
                72.51          4.16        1.3035    0   0   6
                74.16          1.19        1.2786    3   4   2
                75.50          1.27        1.2592    0   5   4
                76.50          1.66        1.2452    0   4   5
                76.94          2.23        1.2391    1   6   1
                78.60          1.26        1.2172    2   4   4
                84.84          1.37        1.1428    2   2   6
                86.43          3.40        1.1259    0   7   2
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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.