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Liroconite

General
Category	Arsenate minerals
Formula (repeating unit)	Cu₂Al[(OH)₄\|AsO₄]·4(H₂O)
IMA symbol	Lro^[1]
Strunz classification	8.DF.20
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	I2/a
Unit cell	a = 12.66, b = 7.57 c = 9.89 [Å]; β = 91.25°; Z = 4
Identification
Color	Bright blue to green
Crystal habit	Typically as striated flattened octahedral or lenticular crystals, also massive to granular
Cleavage	Indistinct on {110} and {011}
Fracture	Irregular/uneven, conchoidal
Mohs scale hardness	2–2+1⁄2
Luster	Vitreous to resinous
Streak	Light blue
Diaphaneity	Transparent, translucent
Specific gravity	2.9–3
Optical properties	Biaxial (−)
Refractive index	n_α = 1.612 n_β = 1.652 n_γ = 1.675
Birefringence	δ = 0.063
2V angle	Measured: 67°
References	^[2]^[3]^[4]

Liroconite is a complex mineral: Hydrated copper aluminium arsenate hydroxide, with the formula Cu₂Al[(OH)₄|As O₄]·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 × 3.0 × 2.0 cm)

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.^[5]

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.^[4]^: 1^[6] The crystal structure consists of a framework of AsO₄ tetrahedra, Jahn-Teller-distorted [CuO₂(OH)₂(H₂O)₂] octahedra and [AlO₂(OH)₄] octahedra.^[7]

References

^ 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.
^ ^a ^b ^c Mindat.org: Liroconite mineral information and data
^ Webmineral data
^ ^a ^b ^c Handbook of Mineralogy
^ Aubrey-Jones, David (2008). "Liroconite".
^ Kolesova, R.V.; Fesenko, E.G. (Dec 1968). "Determination of the crystal structure of Liroconite Cu₂Al[AsO₄](OH)₄ $\cdot$ 4 H₂O" (PDF). Soviet Physics – Crystallography. 13 (3). Rostov University: 396–402.
^ 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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