Liroconite

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	nα = 1.612 nβ = 1.652 nγ = 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|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.

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]