Cornetite | |
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![]() 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 |
IMA symbol | Cne[1] |
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 | [2][3][4][5] |
Cornetite is a phosphate of copper with hydroxyl, named after the geologist Jules Cornet . It was discovered in 1917.
Cornetite is most notably found in the Star of Congo mine, near Lubumbashi.
Cornetite is a rare secondary mineral in some hydrothermal copper deposits.
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]