Potassium tetrachloridocuprate(II) is a salt with chemical formula K2CuCl4, also written as (K+)2·[CuCl4]2−.

The compound is often found as the dihydrate K2CuCl4·2H2O, which is a brilliant greenish blue crystalline solid.

The dihydrate occurs rarely in nature near volcanic vents, e.g. in Mount Vesuvius, as the mineral mitscherlichite; which is named in honor of Eilhardt Mitscherlich (1794–1863), the German crystallographer and chemist who first synthesized the compound.

[1][4] The crystal structure of the dihydrate was partially determined in 1927 by Hendricks and Dickinson[1][4] and refined in 1934 by Chrobak.

[10][11] The phase diagram for the anhydrous system KCl/CuCl2 shows potassium trichloridocuprate KCuCl3 as a congruently-melting compound, but not K2CuCl4.