Cornetite

Phosphate of copper
(repeating unit)Cu3PO4(OH)3IMA symbolCne[1]Strunz classification8.BE.15Dana classification41.03.02.01Crystal systemOrthorhombicCrystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)Space groupPbcaUnit cella = 10.845(10) Å,
b = 14.045(10) Å,
c = 7.081(5) Å; Z = 8IdentificationFormula mass336.63 g/molColorDark blue to green-blueCrystal habitCrystals are short prismaticTwinningOn {h0l}CleavageNone observedMohs scale hardness4.5LusterVitreousDiaphaneityTransparent to translucentSpecific gravity(Measured) 4.10Optical propertiesBiaxial (−)Refractive indexnα = 1.765 nβ = 1.810 nγ = 1.820Birefringenceδ = 0.055 maxPleochroismNon-pleochroic2V angleMeasured: 33°, Calculated: 48°DispersionNoneSolubilitycold HClReferences[2][3][4][5]

Cornetite is a phosphate of copper with hydroxyl, named after the geologist Jules Cornet [fr]. It was discovered in 1917.

Type locality

Cornetite is most notably found in the Star of Congo mine, near Lubumbashi.

Environment

Cornetite is a rare secondary mineral in some hydrothermal copper deposits.

Structure

Unlike related phases such as pseudomalachite, the copper atoms are all five-fold coordinated by oxygen. There are three unique copper sites that are all quite distorted from ideal symmetry. Two are in approximate tetragonal pyramids and the third is essentially a trigonal bipyramidal coordination. Edge sharing polyhedra lead to copper-copper dimer formation, and the overall structure is a three-dimensional network of copper-oxygen polyhedra.[5]

References

Wikimedia Commons has media related to Cornetite.
  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ http://www.mindat.org/min-1131.html Mindat.org
  3. ^ "Cornetite Mineral Data".
  4. ^ http://www.handbookofmineralogy.org/pdfs/cornetite.pdf Handbook of Mineralogy
  5. ^ a b Fehlmann, M.; Ghose, Subrata; Finney, J. J. (1964). "Direct Determination of the Crystal Structure of Cornetite, Cu3PO4(OH)3, by the Monte Carlo Method". J. Chem. Phys. 41 (7): 1910. Bibcode:1964JChPh..41.1910F. doi:10.1063/1.1726182.