Linarite

Linarite is a somewhat rare, crystalline mineral that is known among mineral collectors for its unusually intense, pure blue color. It is formed by the oxidation of galena and chalcopyrite and other copper sulfides. It is a combined copper lead sulfate hydroxide with formula PbCuSO₄(OH)₂. Linarite occurs as monoclinic prismatic to tabular crystals and irregular masses. It is easily confused with azurite, but does not react with dilute hydrochloric acid as azurite does. It has a Mohs hardness of 2.5 and a specific gravity of 5.3 - 5.5.

Linarite
General
Category	Sulfate minerals
Formula (repeating unit)	PbCu[(OH)2|SO4]
Strunz classification	7.BC.65
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m
Unit cell	a = 9.701(2), b = 5.65 c = 4.69 [Å]; β = 102.65°; Z = 2
Identification
Color	Deep azure blue
Crystal habit	Crystals elongated and tabular; in crusts and aggregates
Twinning	Common on {100}, also on {001}
Cleavage	Perfect on {100}, imperfect on {001}
Fracture	Conchoidal
Mohs scale hardness	2.5
Luster	Sub-adamantine, vitreous
Streak	Pale blue
Diaphaneity	Transparent, translucent
Specific gravity	5.3 - 5.5
Optical properties	Biaxial (-)
Refractive index	nα = 1.809 nβ = 1.838 nγ = 1.859
Birefringence	δ = 0.050
Pleochroism	X = pale blue; Y = blue; Z = Prussian blue
2V angle	Measured: 80°
References	[1][2][3]

Linarite was first identified in 1822. It is named after the Linares Plateau, Spain.[1] It occurs in association with brochantite, anglesite, caledonite, leadhillite, cerussite, malachite and hemimorphite.[3]