Langite is a rare hydrated copper sulfate mineral, with hydroxyl, found almost exclusively in druses of small crystals.

Langite was discovered in 1864 and named after the physicist and crystallographer Viktor von Lang (1838–1921), who was Professor of Physics at the University of Vienna, Austria.

[2] Langite belongs to the monoclinic crystal class m, meaning that it has just one mirror plane, and no axes of rotational symmetry.

Different sources give these values: The mineral is pleochroic, with X light yellowish green, Y blue-green and Z sky blue.

[2] Langite is an uncommon but widespread secondary mineral in the oxidised zone of copper sulfide deposits, which may be of post-mine formation.