The crystal structure of a natural sample of disodium magnesium bis(sulfate
) tetrahydrate, Na2Mg(SO4)(2).- 4H(2)O, the Mg end-member of the bloedite-t
ype of mineral, is reported. The structure can be described in terms of par
allel layers built up of MgO2(H2O)(4) and NaO4(H2O)(2) octahedra. Octahedra
l layers are interconnected through SO4 tetrahedra. The two crystallographi
cally independent water molecules give rise to a three-dimensional network
of hydrogen bonds.