Cornetite

Short description: Phosphate of copper

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
|re|er}}| 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 (fr). It was discovered in 1917.

## Contents

* 1 Type locality
* 2 Environment
* 3 Structure
* 4 References

## 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. ↑ "Cornetite Mineral Data". http://webmineral.com/data/Cornetite.shtml.
3. ↑ http://www.handbookofmineralogy.org/pdfs/cornetite.pdf Handbook of Mineralogy
4. ↑ 4.0 4.1 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. doi:10.1063/1.1726182. Bibcode: 1964JChPh..41.1910F.
5. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.

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