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 is Na-birn
_database_code_amcsd 0001300
5.174 2.850 7.336 90 103.18 90 C2/m
atom    x y    z  occ Biso
Mn      0 0    0       0.5
O1   .376 0 .133       1.0
Na   .595 0 .500 .145  1.5
Wat2 .595 0 .500  .30  1.5
Wat3    0 0   .5  .15  1.5