Calcite
Diffraction data computed using the structure from the paper listed below, 
along with the cell parameters refined from the powder pattern of R040170
      Graf D L
      American Mineralogist 46 (1961) 1283-1316
      Crystallographic tables for the rhombohedral carbonates

      CELL PARAMETERS:   4.9828  4.9828 17.0984   90.000   90.000  120.000
      SPACE GROUP: R-3c      

           ATOM        X         Y         Z     OCCUPANCY  ISO(B)
            Ca     0.00000   0.00000   0.00000     1.000     1.300
            C      0.00000   0.00000   0.25000     1.000     0.300
            O      0.25780   0.00000   0.25000     1.000     1.000

            X-RAY WAVELENGTH:     1.541838
            BOUNDS ON TWO THETA:    5.0  90.0
            LIMITS IMPOSED ON THE INDICES ARE:  +/-  3 +/-  3 +/- 15
            MAX. ABS. INTENSITY / VOLUME**2:      26.57631323    
            The INTENSITY cut off value is   1.00

               2-THETA      INTENSITY    D-SPACING   H   K   L
                23.09          8.07        3.8523    0   1   2
                29.41        100.00        3.0369    1   0   4
                31.39          2.45        2.8497    0   0   6
                36.05         13.63        2.4914    1   1   0
                39.47         20.06        2.2828    1   1   3
                43.25         14.18        2.0920    2   0   2
                47.19          6.14        1.9262    0   2   4
                47.47         19.76        1.9153    0   1   8
                48.54         20.01        1.8757    1   1   6
                56.69          3.70        1.6236    2   1   1
                57.53          9.12        1.6021    1   2   2
                60.78          5.26        1.5239    2   1   4
                61.02          2.41        1.5184    2   0   8
                61.37          3.19        1.5107    1   1   9
                63.16          2.28        1.4721    1   2   5
                64.82          6.79        1.4384    3   0   0
                65.51          3.94        1.4249    0   0  12
                69.27          1.51        1.3564    2   1   7
                70.24          2.13        1.3401    0   2  10
                72.96          2.69        1.2966    1   2   8
                77.11          1.93        1.2369    1   1  12
                81.57          2.24        1.1802    2   1  10
                83.96          1.56        1.1525    1   3   4
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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.