Brochantite

Brochantite is a sulfate mineral, one of a number of cupric sulfates. Its chemical formula is Cu4SO4(OH)6.[1][2][3] 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.[3]

Brochantite
General
CategorySulfate minerals
Formula
(repeating unit)		Cu4SO4(OH)6
Strunz classification7.BB.25
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Identification
ColorGreen, emerald green, or black
Crystal habitPrismatic crystals; acicular needle-like crystals; druse
CleavagePerfect [100]
FractureConchoidal - brittle
Mohs scale hardness3.5 - 4.0
LusterVitreous - pearly
StreakPale green
DiaphaneityTransparent to translucent
Specific gravity3.97
Optical propertiesBiaxial (-), 2V measured: 72°
Refractive indexnα = 1.728 nβ = 1.771 nγ = 1.800
Birefringenceδ = 0.072
PleochroismWeak
References[1][2][3]

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.

The mineral is found in a number of locations around the world, notably the southwestern United States (especially Arizona), Serifos in Greece and Chile.

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.[4] 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.
  • Brochantite on Chrysocolla. Locality: Rokana Mine, Kitwe, Copperbelt Province, Zambia . Detail of larger specimen, field of view about 3 x 5 cm.
  • Brochantite on Linarite. Locality: Mujuram, Morocco. Size 8 x 8 cm.

References
  1. Webmineral
  2. Mineral Handbook
  3. Mindat
  4. Leygraf C, Graedel TE. Atmospheric corrosion. New York: Wiley-Interscience; 2000. ISBN 0471372196
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.