Calcite
Diffraction data computed using the structure from the paper listed below, 
along with the cell parameters refined from the powder pattern of R040070
      Markgraf S A, Reeder R J
      American Mineralogist 70 (1985) 590-600
      High-temperature structure refinements of calcite and magnesite
      Sample: T = 24 C

      CELL PARAMETERS:   4.9869  4.9869 17.0496   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     0.936
            C      0.00000   0.00000   0.25000     1.000     0.907
            O      0.25670   0.00000   0.25000     1.000     1.512

            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:      26.74792937    
            The INTENSITY cut off value is   1.00

               2-THETA      INTENSITY    D-SPACING   H   K   L
                23.09          8.36        3.8526    0   1   2
                29.44        100.00        3.0337    1   0   4
                31.48          2.07        2.8416    0   0   6
                36.02         14.36        2.4934    1   1   0
                39.46         18.81        2.2834    1   1   3
                43.22         14.64        2.0933    2   0   2
                47.18          6.50        1.9263    0   2   4
                47.58         19.73        1.9112    0   1   8
                48.58         20.46        1.8742    1   1   6
                56.65          3.42        1.6249    2   1   1
                57.48          9.78        1.6032    1   2   2
                60.76          5.68        1.5244    2   1   4
                61.09          2.63        1.5169    2   0   8
                61.47          2.79        1.5084    1   1   9
                63.15          2.06        1.4723    1   2   5
                64.76          6.70        1.4396    3   0   0
                65.72          3.76        1.4208    0   0  12
                69.30          1.33        1.3560    2   1   7
                70.36          2.30        1.3381    0   2  10
                73.01          2.98        1.2959    1   2   8
                77.29          2.23        1.2345    1   1  12
                81.66          2.54        1.1791    2   1  10
                83.91          1.58        1.1531    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.