The crystal structure described by MgCO3 crystallizes in the monoclinic C2/m space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted pentagonal planar geometry to one O(5), two equivalent O(2), and two equivalent O(3) atoms. In the second Mg site, Mg(2) is bonded to one O(4), one O(6), two equivalent O(2), and two equivalent O(3) atoms to form distorted MgO6 octahedra that share  a cornercorner with one C(2)O4 tetrahedra and corners with six equivalent C(1)O4 tetrahedra. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. There are two inequivalent C sites. In the first C site, C(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form CO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra,  a cornercorner with one C(1)O4 tetrahedra, and  a cornercorner with one C(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-62°. In the second C site, C(2) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form CO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra and corners with two equivalent C(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. There are six inequivalent O sites. In the first O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), and one C(1) atom. In the second O site, O(4) is bonded in a 4-coordinate geometry to one Mg(2), two equivalent Mg(3), and one C(2) atom. In the third O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Mg(3), and one C(2) atom. In the fourth O site, O(6) is bonded in a trigonal planar geometry to one Mg(2) and two equivalent C(1) atoms. In the fifth O site, O(1) is bonded in a bent 120 degrees geometry to one Mg(3), one C(1), and one C(2) atom. In the sixth O site, O(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Mg(2), and one C(1) atom. is represented by the CIF file [CIF]
data_MgCO3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.953
_cell_length_b   5.953
_cell_length_c   8.243
_cell_angle_alpha   79.709
_cell_angle_beta   79.709
_cell_angle_gamma   73.727
_symmetry_Int_Tables_number   1
_cell_volume   273.329
_cell_formula_units_Z   6
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  C  C0  1  0.310  0.959  0.299  1.0
  C  C1  1  0.041  0.690  0.701  1.0
  C  C2  1  0.690  0.041  0.701  1.0
  C  C3  1  0.959  0.310  0.299  1.0
  C  C4  1  0.251  0.251  0.043  1.0
  C  C5  1  0.749  0.749  0.957  1.0
  Mg  Mg6  1  0.527  0.527  0.300  1.0
  Mg  Mg7  1  0.473  0.473  0.700  1.0
  Mg  Mg8  1  0.158  0.158  0.654  1.0
  Mg  Mg9  1  0.842  0.842  0.346  1.0
  Mg  Mg10  1  0.230  0.770  0.000  1.0
  Mg  Mg11  1  0.770  0.230  0.000  1.0
  O  O12  1  0.410  0.088  0.153  1.0
  O  O13  1  0.912  0.590  0.847  1.0
  O  O14  1  0.590  0.912  0.847  1.0
  O  O15  1  0.088  0.410  0.153  1.0
  O  O16  1  0.514  0.158  0.612  1.0
  O  O17  1  0.842  0.486  0.388  1.0
  O  O18  1  0.486  0.842  0.388  1.0
  O  O19  1  0.158  0.514  0.612  1.0
  O  O20  1  0.200  0.799  0.741  1.0
  O  O21  1  0.201  0.800  0.259  1.0
  O  O22  1  0.800  0.201  0.259  1.0
  O  O23  1  0.799  0.200  0.741  1.0
  O  O24  1  0.141  0.141  0.965  1.0
  O  O25  1  0.859  0.859  0.035  1.0
  O  O26  1  0.386  0.386  0.946  1.0
  O  O27  1  0.614  0.614  0.054  1.0
  O  O28  1  0.138  0.138  0.395  1.0
  O  O29  1  0.862  0.862  0.605  1.0
[/CIF]
.
The crystal structure described by MgCO3 crystallizes in the monoclinic C2/m space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted pentagonal planar geometry to one O(5), two equivalent O(2), and two equivalent O(3) atoms. In the second Mg site, Mg(2) is bonded to one O(4), one O(6), two equivalent O(2), and two equivalent O(3) atoms to form distorted MgO6 octahedra that share  a cornercorner with one C(2)O4 tetrahedra and corners with six equivalent C(1)O4 tetrahedra. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. There are two inequivalent C sites. In the first C site, C(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form CO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra,  a cornercorner with one C(1)O4 tetrahedra, and  a cornercorner with one C(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-62°. In the second C site, C(2) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form CO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra and corners with two equivalent C(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 53°. There are six inequivalent O sites. In the first O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), and one C(1) atom. In the second O site, O(4) is bonded in a 4-coordinate geometry to one Mg(2), two equivalent Mg(3), and one C(2) atom. In the third O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Mg(3), and one C(2) atom. In the fourth O site, O(6) is bonded in a trigonal planar geometry to one Mg(2) and two equivalent C(1) atoms. In the fifth O site, O(1) is bonded in a bent 120 degrees geometry to one Mg(3), one C(1), and one C(2) atom. In the sixth O site, O(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Mg(2), and one C(1) atom. is represented by the CIF file [CIF]
data_MgCO3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.953
_cell_length_b   5.953
_cell_length_c   8.243
_cell_angle_alpha   79.709
_cell_angle_beta   79.709
_cell_angle_gamma   73.727
_symmetry_Int_Tables_number   1
_cell_volume   273.329
_cell_formula_units_Z   6
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  C  C0  1  0.310  0.959  0.299  1.0
  C  C1  1  0.041  0.690  0.701  1.0
  C  C2  1  0.690  0.041  0.701  1.0
  C  C3  1  0.959  0.310  0.299  1.0
  C  C4  1  0.251  0.251  0.043  1.0
  C  C5  1  0.749  0.749  0.957  1.0
  Mg  Mg6  1  0.527  0.527  0.300  1.0
  Mg  Mg7  1  0.473  0.473  0.700  1.0
  Mg  Mg8  1  0.158  0.158  0.654  1.0
  Mg  Mg9  1  0.842  0.842  0.346  1.0
  Mg  Mg10  1  0.230  0.770  0.000  1.0
  Mg  Mg11  1  0.770  0.230  0.000  1.0
  O  O12  1  0.410  0.088  0.153  1.0
  O  O13  1  0.912  0.590  0.847  1.0
  O  O14  1  0.590  0.912  0.847  1.0
  O  O15  1  0.088  0.410  0.153  1.0
  O  O16  1  0.514  0.158  0.612  1.0
  O  O17  1  0.842  0.486  0.388  1.0
  O  O18  1  0.486  0.842  0.388  1.0
  O  O19  1  0.158  0.514  0.612  1.0
  O  O20  1  0.200  0.799  0.741  1.0
  O  O21  1  0.201  0.800  0.259  1.0
  O  O22  1  0.800  0.201  0.259  1.0
  O  O23  1  0.799  0.200  0.741  1.0
  O  O24  1  0.141  0.141  0.965  1.0
  O  O25  1  0.859  0.859  0.035  1.0
  O  O26  1  0.386  0.386  0.946  1.0
  O  O27  1  0.614  0.614  0.054  1.0
  O  O28  1  0.138  0.138  0.395  1.0
  O  O29  1  0.862  0.862  0.605  1.0
[/CIF]
.