Cornetite

Cornetite
Cornetite from the type locality, Star of the Congo Mine, Lubumbashi, Haut-Katanga District, Democratic Republic of the Congo. 5.7 × 3.9 × 3.9 cm in size
General
CategoryPhosphate minerals
Formula
(repeating unit)		Cu3PO4(OH)3
IMA symbolCne[1]
Strunz classification8.BE.15
Dana classification41.03.02.01
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPbca
Unit cella = 10.845(10) Å,
b = 14.045(10) Å,
c = 7.081(5) Å; Z = 8
Identification
Formula mass336.63 g/mol
ColorDark blue to green-blue
Crystal habitCrystals are short prismatic
TwinningOn {h0l}
CleavageNone observed
Mohs scale hardness4.5
LusterVitreous
DiaphaneityTransparent to translucent
Specific gravity(Measured) 4.10
Optical propertiesBiaxial (−)
Refractive indexnα = 1.765 nβ = 1.810 nγ = 1.820
Birefringenceδ = 0.055 max
PleochroismNon-pleochroic
2V angleMeasured: 33°, Calculated: 48°
DispersionNone
Solubilitycold HCl
References[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.