Calomel
Diffraction data computed using the structure from the paper listed below, 
along with the cell parameters refined from single crystal data of R070370
      Calos N J, Kennard C H L, Davis R L
      Zeitschrift fur Kristallographie 187 (1989) 305-307
      The structure of calomel, Hg2Cl2, derived from neutron powder data

      CELL PARAMETERS:   4.4280  4.4280 10.8200   90.000   90.000   90.000
      SPACE GROUP: I4/mmm    

           ATOM        X         Y         Z     OCCUPANCY  ISO(B)
            Hg     0.00000   0.00000   0.11900     1.000    11.088
            Cl     0.00000   0.00000   0.33560     1.000     2.304

            X-RAY WAVELENGTH:     1.541838
            BOUNDS ON TWO THETA:    0.0  90.0
            LIMITS IMPOSED ON THE INDICES ARE:  +/-  4 +/-  4 +/-  9
            MAX. ABS. INTENSITY / VOLUME**2:      232.9729676    
            The INTENSITY cut off value is   1.00

               2-THETA      INTENSITY    D-SPACING   H   K   L
                21.69        100.00        4.0981    1   0   1
                28.51         81.01        3.1311    1   1   0
                32.01         10.11        2.7964    1   0   3
                33.12         18.90        2.7050    0   0   4
                40.75         19.04        2.2140    2   0   0
                44.25         20.33        2.0469    1   1   4
                46.63          7.92        1.9479    2   1   1
                46.72         10.55        1.9442    1   0   5
                53.48          7.05        1.7133    2   0   4
                59.00          2.53        1.5655    2   2   0
                63.70          3.11        1.4609    2   1   5
                66.81          2.26        1.4003    3   1   0
                69.36          1.24        1.3550    2   2   4
                76.62          1.20        1.2435    3   1   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.