New Azurite-Malachite Mixture from Peru
Green malachite, Cu2(CO3)(OH)2, is very popular as an ornamental stone, with huge quantities coming every year from deposits in the Katanga Province of the Democratic Republic of Congo. Blue azurite has a similar chemical composition, Cu3(CO2)2(OH)2, but is much more rare. Cabochons of pure azurite are usually quite dark and not very attractive. A blend of the two is much more appealing for jewelry, but this combination is seldom found. Attractive azurite-malachite mixtures are known mainly from old finds in Bisbee and Morenci, both in the U.S. state of Arizona. There was also a find of malachite-azurite-gypsum mixture from Peru’s Moquegua region in 2012 (J. Hyršl, “Malachite-azurite from Peru,” Journal of Gemmology, Vol. 34, No. 7, 2015, p. 564).
Another new azurite-malachite mixture appeared in 2016 and was originally described as from Puno, in southeastern Peru. In fact, it is from Cochapata, in the Cotabambas Province about 50 km southwest of Cuzco, situated in high mountains. According to a dealer who visited the locality, there are several outcrops of oxidized copper veins on a steep hill exploited by artisanal miners. The veins are up to about 20 cm wide, but the parts most useful for cutting are usually only a few centimeters wide. Several tons of the rough have already been sold in Lima to foreign dealers, with the largest piece weighing 80 kg.
Deep blue azurite is the main mineral found today in Cochapata, accompanied by light green malachite and, less commonly, light blue chrysocolla (figure 1). The most attractive specimens have malachite with a banded structure, but some possess a brecciated structure (figure 2). The rarest samples are stalactites of malachite up to 5 cm in length. Some were sliced perpendicular to the elongated growth direction to prepare very attractive stones with an agate-like structure (figure 3).