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Malachite is a hydrated copper carbonate, just like the azurite with which one finds it often associated. But azurite contains less copper and hydroxide molecules than malachite, which is richer in carbonate ions. Malachite is more stable than azurite under the ambiant conditions. Then, malachite is sometimes formed by weathering of azurite, while preserving the crystalline faces of azurite ("pseudomorphosis").
A pseudomorphosis is a mineralogical curiosity that poses many problems to the mineralogists as long as it is not identified: one sees a mineral with crystalline forms that are not typical of this mineral. However, a detail microscopic observation makes it possible to solve this apparent ambiguity and to detect then a pseudomorphosis.
The malachite is a mineral that is formed in the oxidation zones of sulphides copper deposits. Verdagris (that is formed on the objects rich in copper such as bronze) is not malachite but a complex assemblage of organic compound of copper (often copper oxalate).
The malachite crystals are prismatic, even tabular, but generally form stalactitic aggregates and botryoidal nodules. In fact, concretions were formed thanks to successive deposits thanks to a copper-rich aqueous solution, just like the calcium carbonate stalactites and stalagmites found in the caves.
The malachite colour extends from clear green to dark green, according to the size of the microcrystals which composes the mineral. If one saws one of these malachite stalactites, it will be frequent to observe variations of the tonality of the green color, that will show concentric bands of colors (as for agates or the sections of large trees trunks). Each band is thus a particular episode of malachite deposit.
Malachite is relatively abundant in many copper deposits but the beautiful samples are increasingly rare as the oxidation zones of the deposits disappear definitively with mining activities. The province of Katanga in the R.D. of Congo (formely Zaire) and more particularly the western Mashamba mines are some deposits where were discovered large-sized stalactites. One can also quote Tsumeb in Namibia; the district of Bisbee in the USA. The historic deposits of the Ural Mountains (such as Nizhne-Taglisk) is, since centuries, a source of so large quantities of malachite of so beautiful quality that many columns of the large Russian Palaces consist of massive zoned malachite with a beautiful green dark color (i.e., "the malachite room" of the Winter Place in Saint Peterburg’s Hermitage Palace or the hall of Holy Catherine at the Kremlin Palace in Moscow).
In France, the most famous deposit is that of Chessy-les-Mines in the Rhône. It is also present in the mines of Salsigne and Tistoulet in Aude, like in many other mining localities of the Vosges (Ste Marie aux Mines, Silberthal), of the Pyrénées (Costabonne, Cabrières, Irazein), of Brittany, Morvan (Chizeuil), Massif Central (Langeac, Paulhaguet, Kaymar), of the Alps (from the North to the South), Brittany (Carnoët, Huelgoat), Var (Cap Garonne, Fontsante)...
The type of this species and its place of conservation are not definable because this species is well known since Antiquity.
HISTORY : Name inspired from the Greek word "μαλαχε" [malakhe] meaning "mauve", in reference to its color
Species first described in 77 by Caius Plinius Secundus (23-79 AD), an ancient author, naturalist or natural philosopher and naval and military commander
Type-locality: undefined because species already known from the Ancients
CHEMICAL FORMULA : Cu2 (CO3) (OH)2
CRYSTAL SYSTEM : Monoclinic
COLOR : Green, green blackish, light green, dark green
DIAPHANIETY : Translucent to opaque
LUSTER : Adamantine to vitreous
STREAK : Light green
MORPHOLOGIE : Acicular and prismatic crystals, incrustations, stalactitic aggregates
HARDNESS : 3,0-4,0
CHEMICAL CLASS: 3,983
DENSITY : V - Carbonates, nitrates and borates
GROUP : Malachite
STRUNZ CLASS BEFORE 2001 : 5/C.01-20
STRUNZ CLASS AFTER 2001 : 5.BA.10
