{{short description|Copper arsenate mineral}} {{infobox mineral |boxbgcolor=#65c131| name = Cornwallite | boxtextcolor = #fff | image = Cornwallite-178955.jpg | imagesize = 260px | alt = | caption = Cornwallite in a vug from Pastrana, Murcia, Spain (size: 4.3 × 3.7 × 2.2 cm) | category = Arsenate mineral | formula = Cu<sub>5</sub>(AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub> | IMAsymbol = Cnw<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | strunz = 8.BD.05 | dana = 41.4.2.2 | system = Monoclinic | class = Prismatic (2/m) <br/><small>(same H-M symbol)</small> | symmetry = ''P2''<sub>1</sub>/c | unit cell = a = 17.33&nbsp;Å, b = 5.82&nbsp;Å, <br/>c = 4.60&nbsp;Å; β = 92.22°; Z&nbsp;=&nbsp;2 | color = Verdigis green, blackish-green, emerald-green | habit = Microcrystalline radial fibrous, botryoidal to globular crusts | twinning = | cleavage = Distinct in one direction | fracture = Conchoidal | tenacity = Brittle | mohs = 4.5 | luster = Sub-vitreous, resinous, waxy | streak = Apple green | diaphaneity = Translucent to opaque | gravity = 4.17 | density = | polish = | opticalprop = Biaxial (+/−) | refractive = n<sub>α</sub> = 1.810 – 1.820 n<sub>β</sub> = 1.815 – 1.860 n<sub>γ</sub> = 1.850 – 1.880 | birefringence = δ = 0.040 – 0.060 | pleochroism = | 2V = Measured: 30° to 50° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = <ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Cornwallite Mineralienatlas]</ref><ref name=HBM>[http://rruff.info/doclib/hom/cornwallite.pdf Cornwallite in the Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-1133.html Cornwallite on Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Cornwallite.shtml Cornwallite data on Webmineral]</ref> }} '''Cornwallite''' is an uncommon copper arsenate mineral with formula Cu<sub>5</sub>(AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>. It forms a series with the phosphate pseudomalachite and is a dimorph of the triclinic cornubite. It is a green monoclinic mineral which forms as radial to fibrous encrustations. [[File:Cornwallite-Baryte-54193.jpg|thumb|left|Botryoidal, green cornwallite in a gossan with white baryte from Caldbeck Fells, Cumbria (7.6 × 5.1 × 4.7 cm)]]

==Discovery and occurrence==

It was first described in 1846, for an occurrence in Wheal Gorland, St Day United Mines of the St Day District, Cornwall, England.<ref name=Mindat/> It occurs as secondary mineral in the oxidized zone of copper sulfide deposits. Associated minerals include olivenite, cornubite, arthurite, clinoclase, chalcophyllite, strashimirite, lavendulan, tyrolite, spangolite, austinite, conichalcite, brochantite, azurite and malachite.<ref name=HBM/> {{clear left}}

==See also== * Kernowite, another mineral named after Cornwall

==References== {{Portal|Cornwall}} {{Reflist}}

Category:Arsenate minerals Category:Monoclinic minerals Category:Minerals in space group 14