Double Copper Selenates

Tutton has investigated the crystallographic properties of double selenates of the series R₂SeO₄,CuSeO₄,6H₂O, R representing potassium, rubidium, caesium, or ammonium. They are isomorphous with the monoclinic double salts formed by cupric sulphate with the sulphates of potassium, rubidium, caesium, and ammonium.