cornwallite

{{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 = Cu₅(AsO₄)₂(OH)₄

| IMAsymbol = Cnw{{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}}

| strunz = 8.BD.05

| dana = 41.4.2.2

| system = Monoclinic

| class = Prismatic (2/m)
(same H-M symbol)

| symmetry = P2₁/c

| unit cell = a = 17.33 Å, b = 5.82 Å,
c = 4.60 Å; β = 92.22°; Z = 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_α = 1.810 – 1.820 n_β = 1.815 – 1.860 n_γ = 1.850 – 1.880

| birefringence = δ = 0.040 – 0.060

| pleochroism =

| 2V = Measured: 30° to 50°

| dispersion =

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| melt =

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| references = [https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Cornwallite Mineralienatlas][http://rruff.info/doclib/hom/cornwallite.pdf Cornwallite in the Handbook of Mineralogy][http://www.mindat.org/min-1133.html Cornwallite on Mindat.org][http://www.webmineral.com/data/Cornwallite.shtml Cornwallite data on Webmineral]

}}

Cornwallite is an uncommon copper arsenate mineral with formula Cu₅(AsO₄)₂(OH)₄. 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 with white baryte from Caldbeck Fells, Cumbria (7.6 × 5.1 × 4.7 cm)]]