Ziesite is a copper with formula: β-Cu2V2O7. It was discovered in 1980 as monoclinic crystals occurring as volcanic sublimates around fumaroles , El Salvador. It is named after Emanuel George Zies (1883–1981), an American geochemist who studied Izalco in the 1930s.
Closely related is blossite , also a copper vanadate with formula of α-Cu2V2O7. It forms orthorhombic crystals. Blossite was also first described for specimens from the Izalco volcano.
Ziesite and blossite are polymorphs , different crystal structure for the same chemical composition and are quite similar in physical properties.
Associated minerals include stoiberite , shcherbinaite, mcbirneyite and chalcanthite