Ziesite

Ziesite
General
Category	Vanadate mineral
Formula (repeating unit)	β-Cu2V2O7
Strunz classification	8.FA.10
Crystal symmetry	Monoclinic prismatic H-M symbol: (2/m) Space group: A2/a
Unit cell	a = 7.68 Å, b = 8 Å, c = 10.09 Å; β = 110.27°; Z=2
Identification
Color	Black; reddish brown to dark reddish brown in transmitted light; white in reflected light
Crystal habit	Anhedral crystals and incrustations
Crystal system	Monoclinic
Cleavage	None
Luster	Metallic
Streak	Red brown
Diaphaneity	Opaque
Specific gravity	3.86
Optical properties	Biaxial
Refractive index	2.055
References

Ziesite is a copper vanadate mineral with formula: β-Cu₂V₂O₇. It was discovered in 1980 as monoclinic crystals occurring as volcanic sublimates around fumaroles in the crater of the Izalco Volcano, El Salvador. It is named after Emmanuel G. 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, bannermanite, fingerite, mcbirneyite, blossite, chalcocyanite and chalcanthite.