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Cornwallite

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Clara Mine, Rankach valley, Oberwolfach, Wolfach, Black Forest, Baden-Württemberg, Germany
© Stephan Wolfsried

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Formula:
Cu
 
5
[(OH)
 
2
|AsO
 
4
]
 
2
System:MonoclinicColour:Verdigis green, ...
Hardness:4½
Name:Named after Cornwall, England, wherein lies the type locality.
Dimorph of:Cornubite


The monoclinic dimorph of Cornubite.

A secondary mineral formed by the oxidation of arsenical copper ores.

Classification of Cornwallite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:7/B.11-40
Nickel-Strunz 10th (pending) edition ID:8.BD.05

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
Dana 8th edition ID:41.4.2.2

41 : ANHYDROUS PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
4 : (AB)5(XO4)2Zq
Hey's CIM Ref.:20.1.4

20 : Arsenates (also arsenates with phosphate, but without other anions)
1 : Arsenates of Cu
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Type Occurrence of Cornwallite

Type Locality:Wheal Gorland, St Day United Mines (Poldice Mines), Gwennap area, Camborne - Redruth - St Day District, Cornwall, England, UK
Place of Conservation of Type Material:The Natural History Museum, London, England, MI 1985,1754.
Year of Discovery:1846

Occurrences of Cornwallite

Geological Setting:Found in the oxidized zones of copper deposits.

Physical Properties of Cornwallite

Lustre:Vitreous
Diaphaneity (Transparency):Translucent, Opaque
Comment:Satiny or rough on surfaces from terminations of minute crystals.
Colour:Verdigis green, blackish-green, emerald-green; emerald-green in transmitted light.
Streak:Apple green
Hardness (Mohs):4½
Cleavage:Distinct/Good
On one direction.
Fracture:Irregular/Uneven, Conchoidal
Density (measured):4.17 g/cm3
Density (calculated):4.64 g/cm3

Crystallography of Cornwallite

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:P21/b {P1 1 21/b} {P21/c} {P1 21/c 1} {P21/a}
Cell Parameters:a = 17.33Å, b = 5.82Å, c = 4.6Å
β = 92.22°
Ratio:a:b:c = 2.978 : 1 : 0.79
Unit Cell Volume:V 463.61 ų (Calculated from Unit Cell)
Z:2
Morphology:Microcrystalline, radial fibrous botyroidal to globular and vitreous crusts. Less common as rounded tabular to blocky crystals.

Optical Data of Cornwallite

Type:Biaxial (+/-)
RI values: nα = 1.810 - 1.820 nβ = 1.815 - 1.860 nγ = 1.850 - 1.880
2V:Measured: 30° to 50°, Calculated: 34°
Maximum Birefringence:δ = 0.040 - 0.060

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Very High
Dispersion:r > v

Chemical Properties of Cornwallite

Formula:
Cu
 
5
[(OH)
 
2
|AsO
 
4
]
 
2
Essential elements:As, Cu, H, O
All elements listed in formula:As, Cu, H, O

Relationship of Cornwallite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
8.BD.05Pseudomalachite
Cu
 
5
[(OH)
 
2
|PO
 
4
]
 
2
8.BD.05Reichenbachite
Cu
 
5
[(OH)
 
2
|PO
 
4
]
 
2
8.BD.10Arsenoclasite
Mn
2+
5
[(OH)
 
2
|AsO
 
4
]
 
2
8.BD.10Gatehouseite
Mn
2+
5
[(OH)
 
2
|PO
 
4
]
 
2
8.BD.15Parwelite
Mn
 
10
Sb
 
2
As
 
2
Si
 
2
O
 
24
8.BD.20Reppiaite
Mn
2+
5
[(OH)
 
2
|VO
 
4
]
 
2
8.BD.25Ludjibaite
Cu
 
5
[(OH)
 
2
|PO
 
4
]
 
2
8.BD.30Cornubite
Cu
 
5
[(OH)
 
2
|AsO
 
4
]
 
2
Related Minerals - Hey's Index Grouping:

- +
20.1.1Lammerite
Cu
 
3
[AsO
 
4
]
 
2
20.1.2Olivenite
Cu
 
2
[OH|AsO
 
4
]
20.1.3Clinoclase
Cu
 
3
[(OH)
 
3
|AsO
 
4
]
20.1.5Cornubite
Cu
 
5
[(OH)
 
2
|AsO
 
4
]
 
2
20.1.6Chlorotile (of Frenzel)
20.1.7Geminite
Cu
 
2
[As
 
2
O
 
7
] · 3H
 
2
O
20.1.8Euchroite
Cu
 
2
[OH|AsO
 
4
] · 3H
 
2
O
20.1.9Strashimirite
Cu
 
8
[OH|AsO
 
4
]
 
4
 · 5H
 
2
O
20.1.10Arhbarite
Cu
 
2
Mg[(OH)
 
3
|AsO
 
4
]
20.1.11Lindackerite
CuCu
 
4
[HAsO
 
4
|AsO
 
4
]
 
2
 · 8-9H
 
2
O
20.1.12Conichalcite
CaCu[OH|AsO
 
4
]
20.1.13Liroconite
Cu
 
2
Al[(OH)
 
4
|AsO
 
4
] · 4H
 
2
O
20.1.14Ceruleite
Cu
 
2
Al
 
7
[(OH)
 
13
|(AsO
 
4
)
 
4
] · 11.5H
 
2
O
20.1.15Chenevixite
Cu
 
2
Fe
3+
2
[(OH)
 
2
|AsO
 
4
]
 
2
20.1.16Arthurite
CuFe
3+
2
[(OH,O)|(AsO
 
4
,PO
 
4
,SO
 
4
)]
 
2
 · 4H
 
2
O

Other Names for Cornwallite

Synonyms:
Erinite (of Haidinger)
Other Languages:
German:Cornwallit
Russian:Корнваллит
Spanish:Cornwallita

Other Information

Other Information:Soluble in nitric acid.
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Cornwallite

Reference List:Haidinger (1828) Annalen der Physik, Halle, Leipzig: 14: 228 (as Erinite).

Haidinger (1828) Philosophical Magazine and Journal of Science: 4: 154 (as Erinite).

Turner (1828) Philosophical Magazine and Journal of Science: 4: 155.

Zippe (1847) Konigliche boehmische Gesellschaft der Wissenschaften, Prague, Abh.: [5], 4: 649.

Greg, R.P. and Lettsom, W.G. (1858) Manual of the Mineralogy of Great Britain and Ireland. 483pp., London: 321.

Church (1868) Journal of the Chemical Society, London: 21: 276.

Hillebrand and Washington (1888) American Journal of Science: 35: 299.

Larsen, E.S. (1921) The Microscopic Determination of the Nonopaque Minerals, First edition, USGS Bulletin 679: 63, 72.

Berry, L.G. (1951) Observations on conichalcite, cornwallite, euchroite liroconite and olivenite. American Mineralogist: 36: 484–503.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 798-799 (as Erinite), 925.

Claringbull, G.F., M.H. Hey, and R.J. Davis (1959) Cornubite, a new mineral dimorphous with cornwallite. Mineralogical Magazine: 32: 1–5.

Neues Jahrbuch für Mineralogie, Monatshefte (1999): 468-480.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2000) Handbook of Mineralogy, Volume IV. Arsenates, Phosphates, Vanadates. Mineral Data Publishing, Tucson, AZ, 680pp.: 129.

Internet Links for Cornwallite

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    Localities for Cornwallite

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