Atacamite

Atacamite is a mineral species formed through the oxidation of other copper minerals, with the particularity that requires a dry, arid environment with certain salinity conditions.

It is incorrectly said that this mineral received its name in 1802, from the hand of Prince Dmitri of Gallitzin, since the German naturalist Johann Friedrich Blumenbach (1752 - 1840), described and cited it for the first time in his work published in the Handbuch der Naturgeschichte in 1797. The name belongs from the Atacama Desert, in the north of Chile. An arid, dry climate with a lot of copper mining and currently with important lithium mining.

It is a copper hydroxychloride Cu2(OH)3Cl and belongs to the orthorhombic crystal system. Gives name to an extensive Group within the classification of minerals, all of them with chlorine (Cl-) and hydroxyl (OH-), formed by: atacamite, botallackite, clinoatacamite, gillardite, haydeeite, herbertsmithite, hibbingite, iyoite, kapellasite, kempite, leverettite, misakiite, paratacamite, paratacamite-(Mg), paratacamite-(Ni), tondiite and a species not yet identified (Cu-Zn Chloride Hydroxide). Clinoatacamite and botallackite are polymorphs of atacamite, however, although they have the same chemical composition, they have different crystal structures.

It usually occurs as acicular or prismatic crystals with a green colour, between light green to intense green, and it is very easy to confuse with other more common secondary copper minerals such as malachite (carbonate) or brochantite (sulphate). But a more detailed analytical study is required to identify it.

Atacamite is not a very common mineral in Spanish mines, or at least it has not been identified in some of them where the formation conditions are favourable. Stand out the Andalusian atacamite samples from the Estrella mine (Cuevas de Vera), Rodalquilar and Mina Sol (Níjar). Those from the Ferruginosa Mine (Cabo de Palos, Murcia) and the Valencian ones from the Amorosa mine (Villahermosa del Río, Castellón) are well known.

Atacamite crystals from Ferruginosa mine (Cabo de Palos, Murcia). SEM image: Joan Rosell.

This species had not been found in Catalonia until recent studies carried out in a small mine in Ribes de Freser (Girona) by the Grup Mineralogic Català. In this antimony mine, located in the Sant Antoni area, several specimens were found, formed by aggregates of acicular to lanceolated crystals of an apple green colour, with slight bluish tones. Raman spectroscopy analysis indicated that it was this species, and to complicate identification, it sometimes appears mixed with malachite.