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
Category Phosphate minerals
Formula
(repeating unit)		 Cu3PO4(OH)3
Strunz classification 8.BE.15
Dana classification 41.03.02.01
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pbca
Unit cell a = 10.845(10) Å,
b = 14.045(10) Å,
c = 7.081(5) Å; Z = 8
Identification
Formula mass 336.63 g/mol
Color Dark blue to green-blue
Crystal habit Crystals are short prismatic
Twinning On {h0l}
Cleavage None observed
Mohs scale hardness 4.5
Luster Vitreous
Diaphaneity Transparent to translucent
Specific gravity (Measured) 4.10
Optical properties Biaxial (-)
Refractive index nα = 1.765 nβ = 1.810 nγ = 1.820
Birefringence δ = 0.055 max
Pleochroism non-pleochroic
2V angle Measured: 33° , Calculated: 48°
Dispersion none
Solubility cold HCl
References [1][2][3][4]

Cornetite is a phosphate of copper with hydroxyl named after the geologist Jules Cornet. 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.[4]

References

  1. ↑ http://www.mindat.org/min-1131.html Mindat.org
  2. ↑ http://webmineral.com/data/Cornetite.shtml
  3. ↑ http://www.handbookofmineralogy.org/pdfs/cornetite.pdf Handbook of Mineralogy
  4. 1 2 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: 1910. doi:10.1063/1.1726182.
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