Ludwigite from central Sweden: new data and crystal structure refinement

I Ludwigite froln B-bearing iron ores in the Bergslagen area of central Sweden and in the coastal area north of Stockholm has been studied using chemical and single-crystal diffraction techniques. Structure refinements, completed for three crystals showing slightly different A1 contents, in the space group Pbam (agreement factor: 2.42 ~< R ~< 2.79) indicate that: (1) octahedral MI, M2 and M3 bond distances are similar, although the calculated site population suggests that M1 and M2 are nearly completely occupied by Mg whereas M3 also contains Fe 2+ and Fe>; (2) in the M4 octahedron Fe 3§ and A1 dominate over Mg (and Fe2+); and (3) the distortion parameter, BLD, indicates that M3 is the most regular, whereas M4 is the most distorted octahedron