Langite

General

Category: Copper minerals

Formula (repeating unit): Cu4(SO4)(OH)6·2H2O

Strunz classification: 07.DD.10

Dana classification: 31.4.3.1

Crystal symmetry: Monoclinic domatic H-M symbol: (m) Space group: Pc

Unit cell: a = 7.118 Å, b = 6.031 Å, c = 11.209 Å; β = 90.00−90.02°; Z = 2

Identification

Formula mass: 488.32 g

Color: Greenish blue, sky-blue to bluish green

Crystal habit: Crystals scaly, or as crusts; earthy

Crystal system: Monoclinic

Twinning: Common on {110}, typically repeated

Cleavage: {001} perfect, {010} distinct

Fracture: Uneven

Mohs scale hardness: 2.5 to 3

Luster: Vitreous, crusts silky

Streak: Blue green

Diaphaneity: Translucent

Optical properties: Biaxial (-) r>v weak

Refractive index: nα = 1.708 nβ = 1.760 nγ = 1.798

Birefringence: δ = 0.090

Pleochroism: X = c = light yellowish green Y = b = blue-green Z = a = sky blue

Solubility: Insoluble in water, easily soluble in dilute acids or NH4OH

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