Azurite
Azurite from China with large crystals and light surface weathering.
General
Category	Mineral
Chemical formula	Cu3(CO3)2(OH)2
Identification
Molecular Weight	344.67 gm
Color	Light Blue-Azure Blue-Dark Blue
Crystal habit	massive, prismatic, stalactitc, tabular
Crystal system	Monoclinic
Twinning	Rare, across {101}, {102} or {001}
Cleavage	Perfect on the {011}, fair on the {100}
Fracture	Concoidal
Tenacity	brittle
Mohs Scale hardness	3.5 to 4
Luster	vitreous
Birefringence	δ = 0.108
Dispersion	relatively weak
Pleochroism	Visible
Streak	Light Blue
Density	3.77 - 3.89, Average = 3.83

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^[1] 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^[2] 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"). Image File history File links Metadata Size of this preview: 800 × 532 pixelsFull resolution (3008 × 2000 pixel, file size: 3. ... A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... The molecular mass of a substance (less accurately called molecular weight and abbreviated as MW) is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of point groups. ... It has been suggested that twin boundary be merged into this article or section. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For other uses, see Fracture (disambiguation). ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Dispersion of a light beam in a prism. ... Pleochroism is an optical phenomenon in which grains of a rock appear to be different colors when observed at different angles,under a petrographic microscope. ... The streak (also called powder color) of a mineral is the color of the powder produced when it is dragged across a unweathered surface. ... For other uses, see Density (disambiguation). ... This article is about the French city. ... Pliny the Elder: an imaginative 19th Century portrait. ... Naturalis Historia, 1669 edition, title page. ... Categories: Stub | Colors ... Arabic redirects here. ... For other uses of this term see: Persia (disambiguation) The Persian Empire is the name used to refer to a number of historic dynasties that have ruled the country of Persia (Iran). ... A block of lapis lazuli Lapis lazuli is one of the oldest of all gems, with a history of use stretching back 7,000 years. ...

Mineralogy

Azurite ^{[3] [4] [5]} 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. Azurite is soft, with a Mohs hardness of only 3.5 to 4. The specific gravity 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. azurite can easily be identified because it fizzes with hydrochloric acid. In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. ... This article is about the mineral. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Relative density (also known as specific gravity) is a measure of the density of a material. ...

Uses

Pigs

Azurite has been used as a blue mineral pigment for centuries. 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. Natural Ultramarine pigment in powdered form. ... An egg yolk surrounded by the egg white An egg yolk is the part of an egg which serves as the food source for the developing embryo inside. ... This article is about the mineral. ...

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. Natural ultramarine. ... Cennino DAndrea Cennini (c. ...

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 into malachite tend to limit such uses. Heating destroys azurite easily, so all mounting of azurite specimens must be done at room temperature. When tumbled, azurite takes a fine polish, showing a dazzling display of shades of blue and violet. Jewelry (the American spelling; spelled jewellery in Commonwealth English) consists of ornamental devices worn by persons, typically made with gems and precious metals. ...

Ground azurite powder for use as a pigment.

Image File history File links pigment azurite, photographed by Palladian File links The following pages link to this file: Azurite ... Image File history File links pigment azurite, photographed by Palladian File links The following pages link to this file: Azurite ...

Collecting

The intense color of azurite makes it popular as a 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 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. Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. ...

Historical Trivia

The use of azurite and malachite as copper ore indicators led indirectly to the name of the element nickel 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) that resembles malachite. This resulted in occasional attempts to smelt nickeline in the belief that it was copper ore, but such attempts always ended in failure due to high smelting temperatures needed to reduce nickel. In Germany this deceptive mineral came to be known as kupfernickel, literally "copper demon". The Swedish alchemist Baron Axel Fredrik Cronstedt (who had been trained by Georg Brandt, the discoverer of the nickel-like metal cobalt) 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) 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 the German word for "demons"—that is, they are called nickels. For other uses, see Nickel (disambiguation). ... Niccolite or nickeline is a mineral consisting of nickel arsenide, NiAs, containing 43. ... Annabergite is a mineral consisting of a hydrous nickel arsenate, Ni3(AsO4)2 + 8H2O, crystallizing in the monoclinic system and isomorphous with vivianite and erythrite. ... Genera Allosmerus Hypomesus Mallotus Osmerus Spirinchus Thaleichthys Smelts are a family, Osmeridae, of small anadromous fish. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Categories: | | | | ... “Fiend” redirects here. ... For other uses, see Alchemy (disambiguation). ... Baron Axel Fredrik Cronstedt (1722 – 1765) was a Swedish chemist who discovered nickel in 1751. ... Georg Brandt (b. ... For other uses, see Cobalt (disambiguation). ... Events Adam Smith is appointed professor of logic at the University of Glasgow March 25 - For the last time, New Years Day is legally on March 25 in England and Wales. ... Iron meteorites consist overwhelmingly of nickel-iron alloys. ...

Chemistry

Composition

Fresh, unweathered stalactitic azurite crystals showing the exceptionally deep blue of unaltered azurite.

Unit cell of azurite

One of the two coordination environments of copper found in azurite, featuring cis carbonate and hydroxide ions

Trans-[Cu(CO₃)₂(OH)₂]⁴⁻, the other copper coordination environment

Azurite is one of two basic copper(II) carbonate minerals that occur naturally, the other being bright green malachite. Pure copper carbonate is unstable in water, and is not known to exist in nature. Azurite consists chemically of two parts copper(II) carbonate to one part copper(II) hydroxide: Image File history File links Mineraly. ... Image File history File links Mineraly. ... Image File history File links Size of this preview: 739 × 599 pixelsFull resolution (1100 × 892 pixels, file size: 312 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 739 × 599 pixelsFull resolution (1100 × 892 pixels, file size: 312 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Image File history File links Size of this preview: 586 × 599 pixelsFull resolution (1076 × 1100 pixels, file size: 165 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 586 × 599 pixelsFull resolution (1076 × 1100 pixels, file size: 165 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 512 × 599 pixelsFull resolution (940 × 1100 pixels, file size: 164 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 512 × 599 pixelsFull resolution (940 × 1100 pixels, file size: 164 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Wikipedia does not yet have an article with this exact name. ... This article is about the mineral. ...

2CuCO₃ • Cu(OH)₂

Weathering

Azurite is unstable in open air with respect to malachite, and often is pseudomorphically replaced by malachite. The weathering process consists of the replacement of one-fourth of the carbon dioxide (CO₂) units in azurite with units of water (H₂O). This small change transforms the 2-to-1 carbonate-to-hydroxide ratio of azurite into the 1-to-1 ratio of malachite: In geology, a pseudomorph is a mineral compound resulting from a substitution process in which the appearance and dimensions remain constant, but the mineral which makes up the chief component of the compound is replaced by another. ...

2( 2CuCO₃ • Cu(OH)₂ ) + H₂O → 3( CuCO₃ • Cu(OH)₂ ) + CO₂

From the above equation it is reasonable to assume that one factor in why freshly mined azurite begins a slow conversion to malachite is the low vapor pressure of carbon dioxide in open air. Assuming comparable levels of moisture, this moves the equilibrium towards malachite. Storage in a carbon-dioxide rich atmosphere thus would presumably help slow the azurite weathering process by moving the equilibrium point back towards the mineral containing higher levels of CO₂. Apparatus for carrying out acid-base titration. ...

Color

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The trivial difference in composition between azurite and malachite raises an interesting question: How can such a small change in ratios produce such a drastic color difference? Image File history File links Broom_icon. ...

In transition metal minerals such as azurite and malachite, intense colors typically arise from the formation of coordination complexes. A coordination complex is a metal ion (cation) surrounded in a geometrically precise fashion by molecules or ions called ligands. A ligand can be either a polar molecule such as water, or a negatively charged ion (anion) such as carbonate. The formation of a coordination complex often changes significantly both the chemical behavior of a metal ion and its response to light, as described in detail by crystal field theory. The rules for naming of such complexes often result in long, archaic-sounding names. In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. ... Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ... A cation is an ion with positive charge. ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a... A commonly-used example of a polar compound is water (H2O). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... An anion is an ion with negative charge. ... Ball-and-stick model of the carbonate ion, CO32− For other meanings, see Carbonate (disambiguation) In chemistry, a carbonate is a salt or ester of carbonic acid. ... Crystal field theory is used to describe the electronic structure of transition metal complexes. ... Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ...

For example, copper(II) ions in solution tend to gather four polar molecules around in the shape of a flat (coplanar) square^[6], with the more negative ends of the molecules pointed towards the copper ion: A set of points is said to be coplanar if and only if they lie on the same geometric plane. ... Electric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. ...

 +X- -X+ Cu++ +X- -X+ 

While it is easy to see how the charge of the copper(II) could attract the more negative end of such molecules, the flat arrangement (versus the more intuitive tetrahedral arrangement) is a consequence of the strong shaping effects of electron orbitals within the incomplete inner (transition) electron shell of the copper(II) ion. Realizing that the inner shell electrons that control ligand positions are the same ones that capture light makes the powerful impact of the ligands on color easier to understand. Just as passengers can unexpectedly rock a large sightseeing boat rushing to view a spectacular sight on one side, the redistribution of inner electrons due to the presence of enticing ligands can create a precise distribution of charge that selectively captures particular colors or, more precisely the quanta or photons of those colors.^[7] A tetrahedron (plural: tetrahedra) is a polyhedron composed of four triangular faces, three of which meet at each vertex. ... Electron atomic and molecular orbitals In atomic physics, an electron orbital (or simply orbital) is the description of the behavior of an electron in an atom or molecule according to quantum mechanics. ... In physics quanta is the plural of quantum. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ...

In the absence of ligands such as water, copper(II) ions are, rather surprisingly, colorless. When water molecules become available in sufficient numbers, they attach to the corners (X's) shown above to give the blue color typical of copper sulfate dissolved in water. If ammonia is added to the water, ammonia displaces the four water molecules to form the much deeper blue complex known as tetraamminecopper(II). The addition of ammonia thus provides a simple and vivid test for the presence of copper(II) in a solution. In both of these complexes the more negative oxygen or nitrogen atoms are closer to the copper(II) ion and coplanar with it—that is, the oxygens or nitrogens form the corners of the squares. The more distant hydrogens are relatively unaffected by the electron orbital geometry of the copper(II) ion, and so may lie above or below the surface of the square: Copper (II) sulfate (CuSO4) is the most common copper salt, made by the action of sulfuric acid on the base copper oxide. ... For other uses, see Ammonia (disambiguation). ... Copper has played a significant part in the history of mankind, which has used the easily accessible uncompounded metal for nearly 10,000 years. ...

 H H H H H H H H | |/ | |/ O O H-N N-H Cu++ Cu++ O O H-N N-H /| | /| | H H H H H H H H tetraaquacopper(II) tetraamminecopper(II) 

In contrast to solutions, the ways in which ligands can surround a metal ion in a crystal are constrained by way atoms and molecules are arranged within that crystal. Thus while azurite and malachite are constructed from the same set of copper(II) ions and potential ligands (specifically CO₃^2- carbonate ions and OH^- hydroxide ions), their different crystal structures result in unique geometries in the way those ligands cluster around the copper(II) ions. Specifically, azurite contains two unique copper(II) coordination complexes, and malachite contains an entirely different pair of copper(II) coordination complexes. Since none of these coordination geometries are shared between the two minerals, it can be deduced that one of the two copper(II) coordination species in azurite is responsible for the deep blue color. This species is lost when azurite converts to malachite, resulting in an abrupt switch to the bright green coloration of the malachite complexes.

Of all four of these coordination geometries, only one has the flat coplanar geometry characteristic of many other blue copper complexes. All of the other copper(II) species in both azurite and malachite are either pyramidal, with one additional ligand attached above the square, or octahedral, with two additional ligands attached above and below the square. The only square coplanar complex occurs in one-third of the azurite copper(II) ions and looks like this: This is about the polyhedron. ... An octahedron (plural: octahedra) is a polyhedron with eight faces. ...

 OH- CO3-- Cu++ CO3-- OH- transdicarbonatotransdihydroxocuprate(II) -4 

The similarity of this species to the blue water and ammonia complexes makes it the best candidate for providing the intense blue of azurite.

For readers interested in viewing azurite^[8]and malachite^[9] crystal structures interactively, a JavaMage animation of these and other minerals is available at the Loyola University's Interactive Minerals website, created by Steve Pavkovic.

Synthesis

An idea of just how intense the blue of the azurite complex is can be obtained by slowly dripping a small quantity of copper sulfate solution into a saturated solution of sodium carbonate while stirring rapidly. The result is a solution whose blue is so intense that the equivalent amount of copper solution in ammonia literally pales in comparison. The most likely culprit in this case is a close relative of the azurite species, but with water (H₂O) replacing the hydroxide anions (OH^-): Copper (II) sulfate (CuSO4) is the most common copper salt, made by the action of sulfuric acid on the base copper oxide. ... In chemistry, saturation has four different meanings: In physical chemistry, saturation is the point at which a solution of a substance can dissolve no more of that substance. ... Sodium carbonate (also known as washing soda or soda ash), Na2CO3, is a sodium salt of carbonic acid. ... For other uses, see Ammonia (disambiguation). ...

 H2O CO3-- Cu++ CO3-- H2O transdicarbonatotransdiaquacuprate(II) -2 

The above complex is metastable even at very low concentrations, in the sense that a solution of it looks and behaves very much like a supersaturated solution of azurite. If left overnight in an open container, the complex decomposes through the formation of small crystals of azurite on the sides of the container, leaving the carbonate solution once again colorless. Including the sodium cations that balance the charge of the complex, the crystallization reaction is: Metastability in molecules is the ability of a non-equilibrium chemical state to persist for a long period of time. ... In physics, the term supersaturation or oversaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under existing circumstances. ...

3( Na₂(Cu(CO₃)₂(H₂0)₂) ) → 2CuCO₃•Cu(OH)₂ + 2Na₂CO₃ + 2NaHCO₃ + 4H₂O

In other words, when the azurite forms the surplus carbonate anions and water molecules bound to the copper(II) cations are returned to the solution, with a slight net increase in acidity (buffered by the formation of bicarbonate anions) to balance the formation of copper hydroxide in the azurite crystals. Acidity is a controversial novelette written for the popular South Asian website Chowk. ... For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Copper hydroxide is a precipitate with the formula CuOH. It can be produced by adding a small amount of sodium hydroxide (NaOH) to a dilute solution of copper sulfate (CuSO4. ...

Toxicity

All copper minerals are toxic and should not be ingested. However, the toxicity risk is far less than that of heavy metal minerals such as cinnabar (mercury sulfide), so ordinary handling of azurite poses no significant threat. In common with soluble copper minerals and copper metal itself, azurite poses a significant toxicity threat to aquatic life and should not be used as a decorative stone in fresh or (especially) salt-water aquariums. A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. ... Cinnabar, sometimes written cinnabarite, is a name applied to red mercury(II) sulfide (HgS), or native vermilion, the common ore of mercury. ...

References

See also

• List of minerals

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Azurite