Atacamite
Atacamite, or copper chloride hydroxide, Cu2Cl(OH)3, is a copper halide mineral. At its best, for collectors, it forms brilliantly clear, well-formed green crystals that are slender and prismatic. Its color may be reminiscent of emeralds, but at Mohs hardness of 3 to 3.5, it is much, much so er than emeralds (Mohs 7.5 to 8). Its color can vary from yellow-green to blackish green. While it may grow clusters of prismatic orthorhombic crystals, it may also be found in brous, granular, or massive forms.
Atacamite has several polymorphs. Polymorphs are elements or compounds that can take on di erent forms resulting in very di erent properties despite having the same chemical formula. For instance, carbon can form a two-dimensional sheet-like structure that is one of the so est of minerals (graphite), or—under intense heat and pressure—it can form a three-dimensional isometric structure that is the hardest of minerals (diamond).
Polymorphs of atacamite include paratacamite, clinoatacamite, and botallackite.
Atacamite is a secondary mineral. at is, it forms from the alteration of other copper minerals through oxidation, or weathering. Many minerals weather to create di erent minerals under moist conditions, but atacamite occurs in very arid, desert conditions. It o en occurs in association with other secondary copper minerals such as cuprite, linarite, malachite, chrysocolla, and brochantite.
In fact, it is o en confused with brochantite.
Atacamite is relatively rare and, compared to other minerals, is found in few locations. But where it is found, it may be found in some abundance, particularly in such areas of extreme and continuous dryness as the Atacama Desert in northern Chile (the “type locality” where it was originally found and described), South Australia, and Boleo, Mexico.