Brochantite

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Brochantite
Brochantite.jpg
General
Category Sulfate minerals
Formula
(repeating unit)
Cu4SO4(OH)6
Strunz classification 7.BB.25
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Identification
Color Green, emerald green, or black
Crystal habit Prismatic crystals; acicular needle-like crystals; druse
Cleavage Perfect [100]
Fracture Conchoidal - brittle
Mohs scale hardness 3.5 - 4.0
Luster Vitreous - pearly
Streak Pale green
Diaphaneity Transparent to translucent
Specific gravity 3.97
Optical properties Biaxial (-), 2V measured: 72°
Refractive index nα = 1.728 nβ = 1.771 nγ = 1.800
Birefringence δ = 0.072
Pleochroism Weak
References [1][2][3]

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]

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.

Gallery[edit]

References[edit]

  1. ^ a b Webmineral
  2. ^ a b Mineral Handbook
  3. ^ a b c Mindat
  4. ^ Leygraf C, Graedel TE. Atmospheric corrosion. New York: Wiley-Interscience; 2000. ISBN 0471372196

External links[edit]