malachite(redirected from Green carbonate of copper)
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malachite(măl`əkīt), a mineral, the green basic carbonate of copper occurring in crystals of the monoclinic system or (more usually) in masses. It is translucent or opaque; the luster is silky, vitreous, adamantine, or dull. It takes a good polish. An important ore of copper, it also serves as a gem and for various ornamental purposes and, when finely ground, as a pigment. It is found associated with other ores of copper (especially azuriteazurite
, blue mineral, the basic carbonate of copper, occurring in monoclinic crystals or masses that range from transparent to translucent and opaque. It is usually associated with malachite, which it resembles except in color; when the two minerals are very closely
..... Click the link for more information. ) in various parts of the United States and in Chile, Russia, Congo (Kinshasa), Zimbabwe, and Australia.
a carbonate mineral; composition Cu2[Co3] (OH)2 and containing 57.4 percent Cu. Additional (OH)1— anions in the crystalline structure of malachite are bonded to Cu2+ ions, which are surrounded in one plane by two (OH)1— and two O2+ ions belonging to the (CO3)2- carbonate anion. The most common admixtures are Zn (which isomorphically substitutes for Cu), CaO, SiO2, and Fe2O3.
Malachite crystallizes in the monoclinic system. Crystals, which are acicular or prismatic, are rare. Common formations of malachite are cryptocrystalline or microcrystalline reniform incrustations and stalactitic aggregates, which are evenly banded and divergently fibrous. Earthy malachite masses are known as green copper carbonates. The color of malachite ranges from bright green and bluish green to dark green and sometimes even brownish green. The changes that occur in color in the various zones and layers of reniform masses of malachite create very beautiful and fanciful designs along cut and polished planes. Malachite has a hardness of 3.5-4.0 on Mohs’ scale and a density of 3,900-4, 100 kg/m3.
In nature, malachite occurs in the upper oxidized zones of sulfide copper ores. Large accumulations of solid malachite are extremely rare and form during the replacement of limestone by copper sulfate in the oxidation zone of massive copper deposits. Such accumulations (up to 50 m) were worked in the Urals (in the vicinity of Nizhnii Tagil) during the 18th and 19th centuries; other deposits containing ornamental malachite are located in Chile. Solid malachite is a valuable ornamental material and is used to make jewelry and decorative objects (insets, beads, veneer for table tops, vases, column facings). Large articles are faced with thin malachite plates, which are matched according to design and pasted onto a matrix made of metal or other material (“Russian mosaic”). All ornamental objects and large articles are usually fashioned from Ural malachite (The Hermitage in Leningrad, various palace-museums in the USSR and other countries).
Earthy malachite and small accumulations of the pure mineral are used in the manufacture of the valuable paint known as malachite green. Malachite occurring in mixed oxidized ores is used in the smelting of copper.
G. P. BARSANOV