Cornetite is a phosphate of copper with hydroxyl, named after the geologist Jules Cornet [fr].

Cornetite is most notably found in the Star of Congo mine, near Lubumbashi.

Cornetite is a rare secondary mineral in some hydrothermal copper deposits.

Unlike related phases such as pseudomalachite, the copper atoms are all five-fold coordinated by oxygen.

Two are in approximate tetragonal pyramids and the third is essentially a trigonal bipyramidal coordination.