Copper arsenate is an inorganic compound with the chemical formula Cu<sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>÷nH<sub>2</sub>O (n=0,4). It is a blue or bluish-green solid, forming monoclinic crystals.
Anhydrous copper arsenate (Cu<sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>) is found in nature as the mineral lammerite. The tetrahydrate (Cu<sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>÷4H<sub>2</sub>O) occurs naturally as the mineral rollandite.
Copper arsenate can be prepared by reacting disodium hydrogen arsenate and copper(II) chloride in aqueous solution.
Copper arsenate is an insecticide used in agriculture. It is also used as a herbicide, fungicide, and a rodenticide. It is also used as a poison in slug baits.
Basic copper arsenates with the formulas Cu<sub>2</sub>(OH)AsO<sub>4</sub> and Cu<sub>3</sub>(AsO<sub>4</sub>)(OH)<sub>3</sub> have been observed. The former is found naturally as the mineral olivenite.