}} Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is also known as Chessylite after the Chessy-les-Mines near Lyon, France, where striking specimens have been found. The mineral has been known since ancient times, and was mentioned in Pliny the Elder's Natural History under the Greek name kuanos ("deep blue," root of English cyan) and the Latin name caeruleum The blue of azurite is exceptionally deep and clear, and for that reason the mineral has tended to be associated since antiquity with the deep blue color of low-humidity desert and winter skies. The modern English name of the mineral reflects this association, since both azurite and azure are derived via Arabic from the Persian lazhward, an area known for its deposits of another deep blue stone, lapis lazuli ("stone of azure").
Azurite was used as a blue pigment for centuries. Depending on the degree of fineness to which it was ground, and its basic content of copper carbonate, it gave a wide range of blues. It has been known as mountain blue or Armenian stone, in addition it was formerly known as Azurro Della Magna (from Italian). When mixed with oil it turns slightly green. When mixed with egg yolk it turns green-grey. It is also known by the names Blue Bice and Blue Verditer. Older examples of azurite pigment may show a more greenish tint due to weathering into malachite. Much azurite was mislabeled lapis lazuli, a term applied to many blue pigments. As chemical analysis of paintings from the Middle Ages improves, azurite is being recognized as a major source of the blues used by medieval painters. True lapis lazuli was chiefly supplied from Afghanistan during the Middle Ages while azurite was a common mineral in Europe at the time. Sizable deposits were found near Lyons, France. It was mined since the 12th century in Saxony, in the silver mines located there.
Azurite was distinguished from (the much more expensive) purified natural ultramarine blue by heating (as described by Cennino D'Andrea Cennini). Ultramarine withstands heat, whereas azurite turns black (copper oxide). Gentle heating of azurite produces a deep blue pigment used in Japanese painting techniques.
Azurite is one of two basic copper(II) carbonate minerals, the other being bright green malachite. Simple copper carbonate (CuCO3) is not known to exist in nature. In azurite, copper(II) is linked to two different anions, carbonate and hydroxide, the compound has the formula Cu3(CO3)2(OH)2. The optical properties (color, intensity) of minerals such as azurite and malachite are explained in the context of conventional electronic spectroscopy of coordination complexes. Relatively detailed description are provided by Ligand Field Theory. Small crystals of azurite can be obtained by rapidly stirring a few drops of copper sulfate solution into a saturated solution of sodium carbonate and allowing the solution to stand overnight.
Azurite is unstable in open air with respect to malachite, and often is pseudomorphically replaced by malachite. The weathering process effect of the replacement of some the carbon dioxide (CO2) units with water (H2O). This change in the carbonate/hydroxide ratio of azurite into the 1-to-1 ratio of malachite:
From the above equation the conversion of azurite into malachite is attributable to the low partial pressure of carbon dioxide in air. Azurite is also incompatible with aquatic media, such as salt-water aquariums.
Boulder Mining Corporation: 2004 Program Defines new Target Areas and Extends Azurite Hill Gold Discovery South
Jan 19, 2005; VANCOUVER, BRITISH COLUMBIACCNMatthews - Jan. 19, 2005) - Boulder Mining Corporation (TSX VENTURE:BDR) John H. McAdam, President...