|Crystal class||Prismatic (2/m)
(same H-M symbol)
|Color||Green, emerald green, or black|
|Crystal habit||Prismatic crystals; acicular needle-like crystals; druse|
|Fracture||Conchoidal - brittle|
|Mohs scale hardness||3.5 - 4.0|
|Luster||Vitreous - pearly|
|Diaphaneity||Transparent to translucent|
|Optical properties||Biaxial (-), 2V measured: 72°|
|Refractive index||nα = 1.728 nβ = 1.771 nγ = 1.800|
|Birefringence||δ = 0.072|
Brochantite is a sulfate mineral, one of a number of cupric sulfates. Its chemical formula is Cu4SO4(OH)6. Formed in arid climates or in rapidly oxidizing copper sulfide deposits, it was named by Armand Lévy for his fellow Frenchman, geologist and mineralogist A. J. M. Brochant de Villiers.
Crystals of brochantite can range from emerald green to black-green to blue-green, and can be acicular or prismatic. Brochantite is often associated with minerals such as malachite, azurite, and chrysocolla, and may form pseudomorphs with these minerals.
Brochantite is a common corrosion product on bronze sculptures located in urban areas, where atmospheric sulfur dioxide (a common pollutant) is present. Brochantitie forms mainly in exposed areas where weathering prevents accumulation copper ions and enhancement in the acidity of water films. In sheltered areas, the main corrosion product is antlerite.
These long slender crystals, from Bisbee, Arizona, have the highly desirable emerald green color and good luster that is sought after in Brochantite by collectors. Detail of thumbnail specimen, size 2.3 x 2 x .8 cm.
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|Wikisource has the text of the 1911 Encyclopædia Britannica article Brochantite.|