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A vein of acicular, green antlerite crystals from Chuquicamata, Chile (dimensions: 3.5 x 3.4 x 1.8 cm)
Category Sulfate minerals
(repeating unit)
Strunz classification 07.BB.15
Color Bright green, through darker greens to black
Crystal habit tabular and acicular or fibrous. Also found as reniform, massive or granular specimens
Crystal system Orthorhombic bipyramidal
Cleavage Perfect on [010]
Fracture Uneven
Mohs scale hardness 3 to 3.5
Luster Vitreous
Streak Pale green
Diaphaneity Translucent
Specific gravity 3.9
Optical properties Biaxial (+)
Refractive index nα = 1.726 nβ = 1.738 nγ = 1.789
Pleochroism x: yellowish green y: bluish green z: bluish green
References [1][2]

Antlerite is a greenish hydrous copper sulfate mineral, with the formula Cu3(SO4)(OH)4. It occurs in tabular, acicular, or fibrous crystals with a vitreous luster. Originally believed to be a rare mineral, antlerite was found to be the primary ore of the oxidised zones in several copper mines across the world, including the Chuquicamata mine in Chile, and the Antler mine in Arizona, USA from which it takes its name. It is chemically and optically similar in many respects to other copper minerals such as malachite and brochantite, though it can be distinguished from the former by a lack of effervescence in hydrochloric acid.