| Cornetite | |
| Category: | Phosphate minerals |
| Formula: | Cu3PO4(OH)3 |
| Imasymbol: | Cne[1] |
| Molweight: | 336.63 g/mol |
| Strunz: | 8.BE.15 |
| Dana: | 41.03.02.01 |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Pbca |
| Unit Cell: | a = 10.845(10) Å, b = 14.045(10) Å, c = 7.081(5) Å; Z = 8 |
| Color: | Dark blue to green-blue |
| Habit: | Crystals are short prismatic |
| Twinning: | On |
| Cleavage: | None observed |
| Mohs: | 4.5 |
| Solubility: | cold HCl |
| Luster: | Vitreous |
| Refractive: | nα = 1.765 nβ = 1.810 nγ = 1.820 |
| Opticalprop: | Biaxial (−) |
| 2V: | Measured: 33°, Calculated: 48° |
| Dispersion: | None |
| Birefringence: | δ = 0.055 max |
| Pleochroism: | Non-pleochroic |
| Gravity: | (Measured) 4.10 |
| Diaphaneity: | Transparent to translucent |
| References: | [2] [3] [4] [5] |
Cornetite is a phosphate of copper with hydroxyl, named after the geologist . 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.