Covellite

Big Photo

DR Congo
8.90 carats
© Giovanni Scapin 2015

Covellite is named after Niccolo Covelli, Italian mineralogist who discovered the mineral on Mount Vesuvius, Campania, Italy.

Covellite forms opaque masses with vivid iridescent blue colours.

Massive material can be cut into brilliant blue cabochons.
General Information
Chemical Formula
CuS
Michael O’Donoghue, Gems, Sixth edition (2006)
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Photos of natural/un-cut material from mindat.org
Physical Properties of Covellite
Mohs Hardness1.5 to 2
Anthony et al, Handbook of mineralogy (2001)
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Specific Gravity4.6 to 4.76
Anthony et al, Handbook of mineralogy (2001)
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TenacityFlexible
Anthony et al, Handbook of mineralogy (2001) Flexible in thin leavesMore from other references
Cleavage QualityPerfect
Anthony et al, Handbook of mineralogy (2001)
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FractureUneven
Arthur Thomas, Gemstones (2009)
Optical Properties of Covellite
Refractive Index1.45 to 2.62
Arthur Thomas, Gemstones (2009)
Optical CharacterUniaxial/+
Anthony et al, Handbook of mineralogy (2001)
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Birefringence1.17
Arthur Thomas, Gemstones (2009)
PleochroismMarked, deep blue to pale blue.
Anthony et al, Handbook of mineralogy (2001)
DispersionStrong
Anthony et al, Handbook of mineralogy (2001)
Colour
Colour (General)Indigo-blue or darker, commonly highly iridescent, brass-yellow to deep red.
Anthony et al, Handbook of mineralogy (2001)
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Causes of ColourBlue and orange pleochroism, Band theory
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyOpaque
Anthony et al, Handbook of mineralogy (2001)
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LustreResinous,Pearly,Dull (Earthy),Submetallic
Anthony et al, Handbook of mineralogy (2001) Submetallic, inclining to resinous, somewhat pearly on cleavage; subresinous to dull when massive.More from other references
Crystallography of Covellite
Crystal SystemHexagonal
Anthony et al, Handbook of mineralogy (2001)
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HabitForms hexagonal plates as large as 10 cm, flattened, which may exhibit hexagonal striae; as rosettes of nearly parallel plates; commonly massive and foliated.
Anthony et al, Handbook of mineralogy (2001)
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Geological Environment
Where found:Occurs in the secondary enrichment zones of copper deposits.
Michael O’Donoghue, Gems, Sixth edition (2006)
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Further Information
Mineral information:Covellite information at mindat.org
Significant Gem Localities
Italy
 
  • Sardinia
    • Sassari Province
      • Alghero
Peru
 
  • Arequipa
    • Caraveli Province
J. Hyrsl (2012) Gemstones of Peru, p. 49
USA
 
  • Alaska
    • Valdez-Cordova Borough
      • Nizina District
  • Montana
    • Silver Bow Co.
Michael O’Donoghue, Gems, Sixth edition (2006), p. 401
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