# Cornubite

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> Source: https://en.wikipedia.org/wiki/Cornubite
> Source revision: 1197246630
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{{Short description|Copper arsenate mineral}}
{{Infobox mineral
| name = Cornubite
| category = [Arsenate minerals](/source/Arsenate_minerals)
| boxwidth =
| boxbgcolor = 
| image = Cornubite.jpg
| imagesize   = 
| caption = Cornubite from Majuba Hill, Nevada, US. Specimen size 5 cm
| formula = Cu<sub>5</sub>(AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>
| molweight = 
| strunz = 8.BD.30
| dana = 41.04.02.01 
| system = [Triclinic](/source/Triclinic)
| class = Pinacoidal ({{overline|1}}) <br/><small>(same [H-M symbol](/source/H-M_symbol))</small>
| symmetry = ''P''{{overline|1}}
| color = Light or dark green	
| habit = Fibrous, botryoidal, globular or massive, also rare tabular crystals
| lattice = 
| twinning = 
| cleavage = Distinct in two directions
| fracture = 
| tenacity = 
| mohs = 4
| luster = Vitreous
| refractive = N<sub>α</sub> = 1.87, N<sub>β</sub> not determined, N<sub>γ</sub> = 1.90
| opticalprop = [Biaxial](/source/Birefringence) (−)  
| birefringence = r>v
| pleochroism = 
| streak = Light green 
| gravity = 4.64
| density = 
| melt = 
| fusibility = 
| diagnostic = 
| solubility = 
| diaphaneity = Translucent<ref name=Mindat/><ref name=HOM/> to transparent<ref name=Dana/>
| other = Not radioactive
| references = <ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Cornubite Mineralienatlas]</ref><ref name=Mindat>[http://www.mindat.org/min-1132.html Mindat]</ref><ref name=HOM>[http://rruff.geo.arizona.edu/doclib/hom/cornubite.pdf Handbook of Minerals]</ref><ref name=Dana>Gaines et al (1997) Dana's New Mineralogy Eighth Edition, Wiley</ref><ref name=Webmin>[http://www.webmineral.com/data/Cornubite.shtml Webmineral]</ref>}}
'''Cornubite''' is a rare secondary [copper](/source/copper) [arsenate mineral](/source/arsenate_mineral) with formula: Cu<sub>5</sub>(AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>. It was first described for its discovery in 1958 in Wheal Carpenter, [Gwinear](/source/Gwinear-Gwithian), [Cornwall](/source/Cornwall), [England](/source/England), UK.<ref name=AM44>Claringbull, Hey and Davis, ''American Mineralogist'' (1959) 44: 1321</ref>  The name is from Cornubia, the medieval Latin name for Cornwall.<ref name=Mindat/> It is a [dimorph](/source/dimorph) of [cornwallite](/source/cornwallite), and the [arsenic](/source/arsenic) analogue of [pseudomalachite](/source/pseudomalachite).

==Physical properties==
[Cleavage](/source/Cleavage_(crystal)) is distinct in two directions, both perpendicular to the enlarged faces of the tabular crystals, intersecting at about 70°. Cornubite is fairly soft, with [hardness](/source/Mohs_scale_of_mineral_hardness) 4, the same as [fluorite](/source/fluorite), and [specific gravity](/source/specific_gravity) 4.64, which is similar to another copper arsenate, [clinoclase](/source/clinoclase), at 4.38, but much denser than [quartz](/source/quartz), at 2.66.

==Optical properties==
All [triclinic](/source/triclinic) minerals are [biaxial](/source/Birefringence); cornubite is biaxial (−).  Its [refractive indices](/source/Refractive_index) are quite high, close to 1.9, similar to [zircon](/source/zircon) and [garnet](/source/garnet).  It is green, as are many copper minerals, usually translucent, with a vitreous luster and a light green streak.

==Unit cell==
Cornubite belongs to the triclinic crystal class {{overline|1}}, space group P{{overline|1}}, meaning that it has a very low symmetry, with only a center of symmetry and no [mirror planes](/source/Reflection_symmetry) or [axes of symmetry](/source/Rotational_symmetry). In 1984 Sieber, Hofmeister, Tillmans and Abraham reported new data from [microprobe analysis](/source/Electron_microprobe) of cornubite, which gave [unit cell](/source/unit_cell) parameters a = 6.121 Å, b = 6.251 Å, c = 6.790 Å, α = 92.93°, β = 111.3°, γ = 107.47° and Z = 1.<ref name=AM70>American Mineralogist (1985)70: 1333</ref>

==Structure==
The structure is made up of sheets of edge-shared Cu(O,OH)<sub>6</sub> [octahedra](/source/Octahedron), with a copper atom Cu in the middle of the octahedron and either oxygen O or [hydroxyl](/source/hydroxyl) OH at each of the six vertices. These sheets are connected together by AsO<sub>4</sub> groups with an arsenic As atom in the middle and O at each of the four vertices. In the AsO<sub>4</sub> groups three of the Os are shared with octahedra in one octahedral sheet, and the fourth O is shared with an octahedron in the adjacent sheet. [Hydrogen bonds](/source/Hydrogen_bonds) also connect the sheets together.<ref name=Dana/>

==Crystal habit==
Crystals, which are very rare, are tabular, often in aggregates as rosettes. Cornubite is generally fibrous, botryoidal, globular or massive.

==Environment==
Cornubite is a secondary mineral found in the oxidised zone of copper deposits. In Cornwall it is found in [drusy](/source/Druse_(geology)) quartz associated with [malachite](/source/malachite), Cu<sub>2</sub>(CO<sub>3</sub>)(OH)<sub>2</sub>, [olivenite](/source/olivenite), Cu<sub>2</sub>(AsO<sub>4</sub>)(OH), [cuprite](/source/cuprite), Cu<sub>2</sub>O, [cornwallite](/source/cornwallite), Cu<sup>2+</sup><sub>5</sub>(AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>, and [liroconite](/source/liroconite), Cu<sup>2+</sup><sub>2</sub>Al(AsO<sub>4</sub>)(OH)<sub>4</sub>·4H<sub>2</sub>O.<ref name=Dana/> Some of the world's best specimens come from the Majuba Hill Mine in the Antelope District, Nevada, US. Cornubite occurs there as light green botryoidal crusts on [rhyolite](/source/rhyolite) or as balls and crusts on cornwallite, also as coatings on [clinoclase](/source/clinoclase) and [pseudomorphs](/source/pseudomorphs) after [parnauite](/source/parnauite).<ref name=MON>Castor and Ferdock (2004) Minerals of Nevada, Nevada Bureau of Mines and Geology with the University of Nevada Press</ref>  Other associations are with [chalcophyllite](/source/chalcophyllite), [chenevixite](/source/chenevixite), [pseudomalachite](/source/pseudomalachite), [bayldonite](/source/bayldonite), [tyrolite](/source/tyrolite), [azurite](/source/azurite) and [chrysocolla](/source/chrysocolla).<ref name=HOM/>

==Type locality==
The [type locality](/source/Type_locality_(geology)) is Wheal Carpenter, [Gwinear](/source/Gwinear-Gwithian), Cornwall, UK. The [type material](/source/Type_specimen_(mineralogy)) is conserved at the [Natural History Museum, London](/source/Natural_History_Museum%2C_London), reference BM.1958,122.

== References ==
{{commons category| Cornubite}}

{{Reflist}}

== External links ==
Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=13776

Category:Arsenate minerals
Category:Copper(II) minerals
Category:Triclinic minerals
Category:Minerals in space group 2

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Adapted from the Wikipedia article [Cornubite](https://en.wikipedia.org/wiki/Cornubite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Cornubite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.