Liroconite

Liroconite is a complex mineral: Hydrated copper aluminium arsenate hydroxide, with the formula Cu2Al[(OH)4|AsO4]·4(H2O). It is a vitreous monoclinic mineral, colored bright blue to green, often associated with malachite, azurite, olivenite, and clinoclase. It is quite soft, with a Mohs hardness of 2 - 2.5, and has a specific gravity of 2.9 - 3.0.

Vugs in gossan lined with lustrous, blue-green liroconite blades and sparkly, dark blue clinoclase microcrystals from Wheal Gorland (size: 3.4 x 3.0 x 2.0 cm)
Liroconite
General
CategoryArsenate minerals
Formula
(repeating unit)		Cu2Al[(OH)4|AsO4]·4(H2O)
IMA symbolLro[1]
Strunz classification8.DF.20
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupI2/a
Unit cella = 12.66, b = 7.57
c = 9.89 [Å]; β = 91.25°; Z = 4
Identification
ColorBright blue to green
Crystal habitTypically as striated flattened octahedral or lenticular crystals, also massive to granular
CleavageIndistinct on {110} and {011}
FractureIrregular/uneven, conchoidal
Mohs scale hardness2-2+1⁄2
LusterVitreous to resinous
StreakLight blue
DiaphaneityTransparent, translucent
Specific gravity2.9 - 3
Optical propertiesBiaxial (-)
Refractive indexnα = 1.612 nβ = 1.652 nγ = 1.675
Birefringenceδ = 0.063
2V angleMeasured: 67°
References[2][3][4]

It was first identified in 1825 in the tin and copper mines of Devon and Cornwall, England. Although it remains quite rare it has subsequently been identified in a variety of locations including France, Germany, Australia, New Jersey and California.[2]

The type locality for liroconite is Wheal Gorland in St Day, Cornwall in the United Kingdom.[2] The largest crystal specimen on public display is in the Royal Cornwall Museum in Truro.

It occurs as a secondary mineral in copper deposits in association with olivenite, chalcophyllite, clinoclase, cornwallite, strashimirite, malachite, cuprite and limonite.[4]

Structure

Liroconite crystallizes in the monoclinic crystal system. The crystal structure consists of a framework of AsO4 tetrahedra, Jahn-Teller-distorted [CuO2(OH)2(H2O)2] octahedra and [AlO2(OH)4] octahedra.[5]

Unit cell of liroconite

See also

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mindat.org: Liroconite mineral information and data
  3. Webmineral data
  4. Handbook of Mineralogy
  5. Burns, Peter C.; Eby, Ray K.; Hawthorne, Frank C. (1991). "Refinement of the structure of liroconite, a heteropolyhedral framework oxysalt mineral". Acta Crystallogr. C. 47 (5): 916–919. doi:10.1107/S0108270190010939.
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