Azurite
Overview
 
Azurite is a soft, deep blue copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 produced by weathering of copper ore deposits. It is also known as Chessylite after the type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 at Chessy-les-Mines
Chessy, Rhône
Chessy, also known as Chessy-les-Mines, is a commune in the Rhône department in eastern France.Chessy-les-Mines is the type locality of the mineral azurite, also known as "chessylite." The species was redescribed and renamed in 1824 by François-Sulpice Beudant , French mineralogist and...

 near Lyon
Lyon
Lyon , is a city in east-central France in the Rhône-Alpes region, situated between Paris and Marseille. Lyon is located at from Paris, from Marseille, from Geneva, from Turin, and from Barcelona. The residents of the city are called Lyonnais....

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

. The mineral has been known since ancient times, and was mentioned in Pliny the Elder
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

's Natural History under the Greek name kuanos (κυανός: "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.
Unanswered Questions
Encyclopedia
Azurite is a soft, deep blue copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 produced by weathering of copper ore deposits. It is also known as Chessylite after the type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 at Chessy-les-Mines
Chessy, Rhône
Chessy, also known as Chessy-les-Mines, is a commune in the Rhône department in eastern France.Chessy-les-Mines is the type locality of the mineral azurite, also known as "chessylite." The species was redescribed and renamed in 1824 by François-Sulpice Beudant , French mineralogist and...

 near Lyon
Lyon
Lyon , is a city in east-central France in the Rhône-Alpes region, situated between Paris and Marseille. Lyon is located at from Paris, from Marseille, from Geneva, from Turin, and from Barcelona. The residents of the city are called Lyonnais....

, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

. The mineral has been known since ancient times, and was mentioned in Pliny the Elder
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

's Natural History under the Greek name kuanos (κυανός: "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
Azure (color)
The color bleu de France is displayed at right.Bleu de France is a color that has been associated in heraldry with the Kings of France since the 12th century.-Brandeis blue:...

are derived via Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 from the Persian
Persian language
Persian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan, Tajikistan and countries which historically came under Persian influence...

 lazhward (لاژورد), an area known for its deposits of another deep blue stone, lapis lazuli
Lapis lazuli
Lapis lazuli is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color....

 ("stone of azure").

Mineralogy

Azurite crystals are monoclinic, and when large enough to be seen they appear as dark blue prismatic crystals. Azurite specimens are typically massive to nodular, and are often stalactitic in form. Specimens tend to lighten in color over time due to weathering of the specimen surface into malachite
Malachite
Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...

. Azurite is soft, with a Mohs hardness of only 3.5 to 4. The specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 of azurite is 3.77 to 3.89. Azurite is destroyed by heat, losing carbon dioxide and water to form black, powdery copper(II) oxide. Characteristic of a carbonate, specimens effervesce upon treatment with hydrochloric acid.

Pigments

Azurite was used as a blue pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

 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
Italian language
Italian is a Romance language spoken mainly in Europe: Italy, Switzerland, San Marino, Vatican City, by minorities in Malta, Monaco, Croatia, Slovenia, France, Libya, Eritrea, and Somalia, and by immigrant communities in the Americas and Australia...

). When mixed with oil it turns slightly green. When mixed with egg yolk
Egg yolk
An egg yolk is a part of an egg which feeds the developing embryo. The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalazae...

 it turns green-grey. It is also known by the names Blue Bice
Bice
Bice, from the French bis, a word of doubtful origin, originally meaning dark-coloured, was a term applied in English to particular green or blue pigments. In French the terms vert bis and azur bis mean dark green and dark blue respectively...

and Blue Verditer, though Verditer
Copper(II) hydroxide
Copper hydroxide is the hydroxide of the metal copper with the chemical formula of Cu2. Copper hydroxide is a pale blue, gelatinous solid. Some forms of copper hydroxide are sold as "stabilized" copper hydroxide, quite likely a mixture of copper carbonate and hydroxide...

usually refers to a pigment made by chemical process. Older examples of azurite pigment may show a more greenish tint due to weathering into malachite
Malachite
Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...

. Much azurite was mislabeled lapis lazuli
Lapis lazuli
Lapis lazuli is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color....

, a term applied to many blue pigments. As chemical analysis of paintings from the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

 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
Ultramarine
Ultramarine is a blue pigment consisting primarily of a double silicate of aluminium and sodium with some sulfides or sulfates, and occurring in nature as a proximate component of lapis lazuli...

 blue by heating (as described by Cennino D'Andrea Cennini
Cennino D'Andrea Cennini
Cennino d'Andrea Cennini was an Italian painter influenced by Giotto. He was a student of Agnolo Gaddi. Gaddi trained under his father, called Taddeo Gaddi, who trained with Giotto. Cennini was born in Colle Val d'Elsa, Tuscany....

). Ultramarine withstands heat, whereas azurite turns black (copper oxide). Gentle heating of azurite produces a deep blue pigment used in Japanese painting techniques.

Jewelry

Azurite is used occasionally as beads and as jewelry, and also as an ornamental stone. However, its softness and tendency to lose its deep blue color as it weathers limit such uses. Heating destroys azurite easily, so all mounting of azurite specimens must be done at room temperature.

Collecting

The intense color of azurite makes it a popular collector's stone. However, bright light, heat, and open air all tend to reduce the intensity of its color over time. To help preserve the deep blue color of a pristine azurite specimen, collectors should use a cool, dark, sealed storage environment similar to that of its original natural setting.

Prospecting

While not a major ore of copper itself, azurite is a good surface indicator of the presence of weathered copper sulfide
Copper sulfide
Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores....

 ores. It is usually found in association with the chemically very similar malachite, producing a striking color combination of deep blue and bright green that is strongly indicative of the presence of copper ores.

History

The use of azurite and malachite as copper ore indicators led indirectly to the name of the element nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 in the English language. Nickeline, a principal ore of nickel that is also known as niccolite, weathers at the surface into a green mineral (annabergite
Annabergite
Annabergite is an arsenate mineral consisting of a hydrous nickelarsenate, Ni32·8H2O, crystallizing in the monoclinic system and isomorphous with vivianite and erythrite. Crystals are minute and capillary and rarely met with, the mineral occurring usually as soft earthy masses and encrustations. A...

) that resembles malachite. This resemblance resulted in occasional attempts to smelt
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

 nickeline in the belief that it was copper ore, but such attempts always ended in failure due to high smelting temperatures needed to reduce
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 nickel. In Germany this deceptive mineral came to be known as kupfernickel, literally "copper demon
Demon
call - 1347 531 7769 for more infoIn Ancient Near Eastern religions as well as in the Abrahamic traditions, including ancient and medieval Christian demonology, a demon is considered an "unclean spirit" which may cause demonic possession, to be addressed with an act of exorcism...

". The Swedish
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 alchemist Baron Axel Fredrik Cronstedt
Axel Fredrik Cronstedt
Baron Axel Fredrik Cronstedt was a Swedish mineralogist and chemist who discovered nickel in 1751 as a mining expert with the Bureau of Mines. Cronstedt described it as kupfernickel...

 (who had been trained by Georg Brandt
Georg Brandt
-External links:** by Uno Boklund in: Charles C. Gillispie, ed., Dictionary of Scientific Biography , vol. 2, pages 421-422....

, the discoverer of the nickel-like metal cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

) realized that there was probably a new metal hiding within the kupfernickel ore, and in 1751 he succeeded in smelting kupfernickel to produce a previously unknown (except in certain meteorites
Iron meteorite
Iron meteorites are meteorites that consist overwhelmingly of nickel-iron alloys. The metal taken from these meteorites is known as meteoric iron and was one of the earliest sources of usable iron available to humans.-Occurrence:...

) silvery white, iron-like metal. Logically, Cronstedt named his new metal after the nickel part of kupfernickel. An unintended later consequence of his choice is that both Canadian and American coins worth one-twentieth of a dollar are now named after a German term for "kobold
Kobold
The kobold is a sprite stemming from Germanic mythology and surviving into modern times in German folklore. Although usually invisible, a kobold can materialise in the form of an animal, fire, a human being, and a candle. The most common depictions of kobolds show them as humanlike figures the size...

s"—that is, they are called nickels.

Composition

Azurite is one of two basic copper(II) carbonate minerals
Carbonate minerals
Carbonate minerals are those minerals containing the carbonate ion: CO32-.-Anhydrous carbonates:*Calcite group: Trigonal**Calcite CaCO3**Gaspeite CO3**Magnesite MgCO3**Otavite CdCO3**Rhodochrosite MnCO3**Siderite FeCO3**Smithsonite ZnCO3...

, the other being bright green malachite
Malachite
Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...

. 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 descriptions are provided by ligand field theory
Ligand field theory
Ligand field theory describes the bonding, orbital arrangement, and other characteristics of coordination complexes. It represents an application of molecular orbital theory to transition metal complexes. A transition metal ion has nine valence atomic orbitals, five d, one s, and three p orbitals...

. Small crystals of azurite can be obtained by rapidly stirring a few drops of copper sulfate solution into a saturated solution of sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 and allowing the solution to stand overnight.

Weathering

Azurite is unstable in open air with respect to malachite, and often is pseudomorph
Pseudomorph
In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form , resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another...

ically replaced by malachite
Malachite
Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...

. The weathering process involves the replacement of some the carbon dioxide (CO2) units with water (H2O). This changes the carbonate:hydroxide ratio of azurite from 1:1 to the 1:2 ratio of malachite:
2 Cu3(CO3)2(OH)2 + H2O → 3 Cu2(CO3)(OH)2 + CO2


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 saltwater aquariums.
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