Atacamite, the desert mineralNamed in 1802 after one of the globe’s dryest reg…

Atacamite, the desert mineral

Named in 1802 after one of the globe’s dryest regions this beautiful and rare copper mineral is only found in arid saline (since it is a chloride like table salt) regions where primary copper mineralisation consisting of sulphide minerals have been altered by oxygenated groundwater in the upper levels of the deposit. The usual colour is a one of several shades of deep green, though yellow is also occasio0nally known. Crystals are usually needle shaped (called acicular by mineralogists) with striations running down the length and often felted together in a fibrous habit (a word for the usual form of a mineral). It is too soft for jewellery use (3.5 on Mohs scale).

Other than the primary locality in Chile it also occurs near Vesuvius in Italy (where it sublimated from copper rich volcanic gases pouring out of fumaroles), Australia and Arizona. On rare occasions it has been found replacing ancient copper or bronze objects. Further contact with carbonated waters often alters it to malachite which retains the original felted needle shape of the atacamite, a process known as pseudomorphism. The 5.7 x 5 x 4 cm stalactite on country rock matrix in the photo comes from the Lake Thorens region in South Australia.


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Image credit: Rob Lavinsky/
A free paper on its formation conditions: