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Mineral formula: Cu4(SO4)(OH)6

Crystal system: Monoclinic

Crystal habit: prismatic to acicular, elongated, or, more rarely, tabular. Loosely coherent aggregates of acicular crystals; groups and drusy crusts; massive, granular.

Cleavage: perfect on {100}

Fracture: irregular/uneven, conchoidal

Color: green, emerald green, green-black, light green

Luster: vitreous, pearly

Diaphaneity: transparent, translucent

Moh’s scale hardness: 3 ½ - 4

Streak: pale green

Specific gravity: 3.97

Named after: the French geologist and mineralogist, André-Jean-François-Marie Brochant de Villiers, by Serve-Dieu Abailard "Armand" Lévy in 1824.

Type locality: Mednorudyanskoye Copper Deposit, Nizhnii Tagil, Sverdlovsk Oblast, Russia

Geological occurrence:  A common secondary copper hydroxy sulphate, typically found in arid climates or in rapidly oxidizing copper sulfide deposits under low acid conditions. May be observed as pseudomorphs after malachite, azurite and langite, and altered to chrysocolla.