Sodium magnesium sulfate

Sodium magnesium sulfate is a double sulfate of sodium and magnesium. There are a number of different stoichiometries and degrees of hydration with different crystal structures, and many are minerals.
Members include:

Blödite or bloedite: sodium magnesium sulfate tetrahydrate Na₂Mg₂•4H₂O
Disodium magnesium disulfate decahydrate Na₂Mg₂•10H₂O
Disodium magnesium disulfate hexadecahydrate Na₂Mg₂•16H₂O
Na₂SО₄·MgSO₄·2.5H₂O
Konyaite Na₂Mg₂•5H₂O
Löweite Na₁₂Mg₇₁₃•15H₂O.
Vanthoffite Na₆Mg₄
Na₂Mg₂₃ langbeinite form stable from 569.2 to 624.7°C
Na₂Mg₂₃ quenched monoclinic form
Na₂Mg₃₄ orthorhombic form
Na₂Mg₂ triclinic form

Salts containing other anions in addition to sulfate

Na₂Mg₃₂₄•4H₂O
Tychite hexasodium dimagnesium sulfate tetracarbonate Na₆Mg₂SO₄₄
Uklonskovite NaMgSO₄F•2H₂O