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Formula: Cu2Cl(OH)3
Hydroxylhalide, atacamite group
Crystal System: Orthophombic
Specific gravity: 3.745 to 3.776 measured, 3.756 calculated
Hardness: 3 to 3½
Streak: Apple green
Colour: Bright green, dark emerald-green to blackish green; shades of green in transmitted light.
Solubility: Easily soluble in acids
Common impurities: Ca,Co
Environments:
Hydrothermal environments
Fumeroles
Atacamite is a secondary copper mineral formed through the
oxidation of other copper minerals, especially in arid, saline conditions.
It is also found in fumarolic deposits and as a weathering product of sulphides in subsea black smoker deposits
(HOM).
Associated minerals include cuprite,
brochantite,
linarite, caledonite,
malachite, chrysocolla,
paratacamite and botallackite
(HOM).
Atacamite may alter to malachite and
chrysocolla,
creating pseudomorphs
(Mindat).
At Broken Hill, New South Wales, Australia, atacamite is associated with
cerussite, chalcocite
and chrysocolla
(AJM 03.1.34).
At Northparkes, New South Wales, Australia, atacamite occurs in quartz
monzonite associated with
malachite and azurite
(AJM 10.2.55 0.
At the Cams mine (now abandoned), Lake Miranda, Western Australia, atacamite was found on the dumps on
limonite-coated quartz
(AJM 20.1.51-54).
At the Surprise lead mine, Northampton lead-copper field, Western Australia, atacamite forms thin surface coatings on
galena
(AJM 18.1.39).
In Yunnan, China, atacamite has been found as slender, prismatic, dark green, vitreous crystals to 4 mm in a vugs
in a dark, heavy matrix with a slight blue metallic sheen
(AESS).
Atacamite from Yunnan - Image
At the Lily mine, ICA department, Peru, atacamite occurs included in gypsum
(Minrec 42.2.168).
At Bisbee, Arizona, USA, atacamite commonly occurs associated with cuprite
nodules.
It has been found in a cuprite nodule associated with
spangolite, and separately associated with
spangolite and claringbullite
(Minrec 43.1 supplement, pps 14, 17, 33).
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