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Bornite

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Bornite is a one of nature’s most colorful minerals thats are copper iron sulfide named after the Austrian mineralogist Ignaz von Born (1742–91). A major ore of copper, its natural color can be coppery red, coppery brown, or bronze. It can also show iridescent purple, blue, and red splashes of color on broken, tarnished faces, which explains its common name, “peacock ore.” Bornite is also known as “purple copper ore” and “variegated copper ore.” Bornite crystals are uncommon. Although they exhibit orthorhombic symmetry, crystals, when found, are cubic, octahedral, or dodecahedral, often with curved or rough faces. Bornite is frequently compact, granular, or massive and alters readily to chalcocite and other copper minerals upon weathering. It forms mainly in hydrothermal copper ore deposits with minerals such as chalcopyrite , pyrite marcasite , and quartz . It also forms in some silica-poor, intrusive igneous rocks and in pegmatite veins and contact metamorphic zones.

Chemical Properties of Bornite

Chemical Classification Sulfide
Chemical Composition Cu5FeS4

Physical Properties of Bornite

Color Copper-red to pinchbeck-brown, quickly tarnishing to an iridescent purplish surface.
Streak Grey-Black    
Luster Metallic
Diaphaneity Opaque          
Mohs Hardness 3
Specific Gravity 5.0 to 5.1
Diagnostic Properties Color, tarnish, lower hardness than similar minerals. Almost always found in massive occurrences and very rarely as tiny crystals.
Crystal System Orthorhombic
Tenacity Brittle
Parting None
Fracture Irregular/Uneven
Density 5.06 – 5.09 g/cm3 (Measured)    5.09 g/cm3 (Calculated)

Optical Properties of Bornite

Type Anisotropic
Anisotropism Weak
Cleavage Poor/Indistinct In traces on {111}.
Color / Pleochroism Weak
Optical Extinction  
Twinning  
Optic Sign  
Birefringence  
Relief  

Occurrence

Associated with and disseminated in mafic igneous rocks, in contact metamorphic skarn deposits, in pegmatites, in medium- to high-temperature hydrothermal deposits, and in sedimentary cupriferous shales; stable below ∼200 ◦C.

Uses Area

Bornite is a common copper bearing mineral, and is used as an ore of copper when found in copper deposits

Association: Chalcopyrite, pyrite, other copper and iron sulfides, garnet, calcite, wollastonite, quartz.

Distribution

Important localities for fine crystals include:

  • in the USA, from Butte, Silver Bow Co., Montana, and at Bristol, Hartford Co., Connecticut.
  • In England, from the Carn Brea mine, Illogan, and elsewhere in Cornwall.
  • Large crystals from the Mangula mine, Lomagundi district, Zimbabwe.
  • From the Frossnitz Alpe, eastern Tirol, Austria.
  • At Dzhezkazgan, Kazakhstan.
  • In the Nouva mine, Talate, Morocco.
  • Widespread as an important ore mineral of copper, for example at the Magma mine, Superior, Pinal Co., and Bisbee, Cochise Co., Arizona; and Kennicott, Alaska, USA.
  • At Ookiep, Namaqualand, Cape Province; and the Messina mine, Transvaal, South Africa.
  • In Australia, from Mt. Lyell, Tasmania, and Olympic Dam, Roxby Downs, South Australia.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Bornite: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/min-727.html [Accessed 4 Mar. 2019].
Cite this article as: Geology Science. (2019). Bornite. [online] Available at: http://geologyscience.com/minerals/bornite/ [21st October 2019 ]
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