, is a nonstoichiometric olivine-type mineral and shows superstructures with 2c and 3c repeats of the basic olivine structure. The superstructure of laihunite-3M was determined in P21/b (a = unique axis) symmetry with 1889 reflections collected from a twinned specimen. The cell dimensions are a = 4.805(2) Å, b = 10.189(9) Å, c = 17.403(9) Å and α = 91.0(2)°.

The average structure was used as a starting model for the superstructure. Each equivalent octahedral site for Fe atoms in the average structure differentiates into two or three nonequivalent sites in the superstructure, resulting in translation of the c axis three times that of the average structure of olivine. The site occupancies and bond distances of the octahedral sites for cations in the structure indicate the following distribution: M1A (1.0Fe2+), M1B (0.82Fe2+ + 0.18Mg), M2A (0.20Fe2+ + 0.80Fe3+), M2B (0.20Fe2+ + 0.80Fe3+), VA (vacant), and VB (0.67Fe2+).

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