A white crystalline powder, K2SO4, soluble in water and insoluble in ethanol; rhombic or hexagonal; r.d. 2.66; m.p. 1069°C. It occurs naturally as schönite (Strassfurt deposits) and in lake brines, from which it is separated by fractional crystallization. It has also been produced by the Hargreaves process, which involves the oxidation of potassium chloride with sulphuric acid. In the laboratory it may be obtained by the reaction of either potassium hydroxide or potassium carbonate with sulphuric acid. Potassium sulphate is used in cements, in glass manufacture, as a food additive, and as a fertilizer (source of K+) for chloride-sensitive plants, such as tobacco and citrus.