Gadolinium sulphate, Gd₂(SO₄)₃

The Gadolinium sulphate octahydrate, Gd₂(SO₄)₃.8H₂O, is the only hydrate known, and forms monoclinic crystals. The solubility (in parts of anhydrous salt per 100 of water) is as follows: -

0°	10°	14°	25°	34.4°
3.98	3.33	2.80	2.40	2.26

The solubility in a saturated solution of sodium sulphate is such that at 25° C. the solution contains 0.6 gram of anhydrous gadolinium sulphate per litre, gadolinium sodium sulphate, Gd₂(SO₄)₃.Na₂SO₄.2H₂O, being the stable solid phase. The corresponding potassium salt is also known (Benedicks).