Birnessite Post J E, Veblen D R American Mineralogist 75 (1990) 477-489 Crystal structure determinations of synthetic sodium, magnesium and potassium birnessite using TEM and the Rietveld method Sample: K-birn _database_code_amcsd 0001302 5.149 2.843 7.176 90 100.76 90 C2/m atom x y z occ Biso Mn 0 0 0 0.5 O1 .365 0 .136 1.0 K .723 0 .522 .115 1.5 Wat2 .723 0 .522 .275 1.5 Wat3 0 0 .5 .15 1.5