The crystal structures of two forms of Mg3(PO4)2·8H2O, bobierrite (I) and the synthetic polymorph (II), have been determined by single-crystal X-ray diffraction. Crystal data for polymorph I are space group C2/c, a = 4.667(1), b = 27.926(8), c = 10.067(3) Å, β = 105.01(2)°, Z = 4, R = 0.041 for 963 reflections. Crystal data for polymorph II are space group C2/m, a = 10.034(1), b = 13.407(2), c = 4.657(1) Å, β = 105.09(1)°, Z = 2, R = 0.025 for 510 reflections. The structure of polymorph I is closely related to that of the vivianite group, whereas polymorph II is isostructural with vivianite. Both structures consist of octahedral edge-sharing dimers Mg2O6(H2O)4 and independent MgO2(H2O)4 octahedra linked together by PO4 tetrahedra to form complex sheets parallel to (010). The arrangement of these sheets along b is different in the two structures.

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First page of Crystal structures of bobierrite and synthetic Mg<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O
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