Azurite

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Azurite
Azurite - New Nevada Lode, La Sal, Utah, USA.jpg
Azurite from New Nevada lode, La Sal, Utah, USA
General
Category Carbonate mineral
Formula
(repeating unit)		Cu3(CO3)2(OH)2
IMA symbol Azu [1]
Strunz classification 5.BA.05
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/c
Unit cell a = 5.01  Å, b = 5.85 Å
c = 10.35 Å; β = 92.43°; Z = 2
Identification
Formula mass 344.67 g/mol
ColorAzure-blue, dark to pale blue; pale blue in transmitted light
Crystal habit Massive, prismatic, stalactitic, tabular
Twinning Rare, twin planes {101}, {102} or {001}
Cleavage Perfect on {011}, fair on {100}, poor on {110}
Fracture Conchoidal
Tenacity brittle
Mohs scale hardness3.5 to 4
Luster Vitreous
Streak Light blue
Diaphaneity Transparent to translucent
Specific gravity 3.773 (measured), 3.78 (calculated)
Optical propertiesBiaxial (+)
Refractive index nα = 1.730 nβ = 1.758 nγ = 1.838
Birefringence δ = 0.108
Pleochroism Visible shades of blue
2V angle Measured: 68°, calculated: 64°
Dispersion relatively weak
References [2] [3] [4]

Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. During the early 19th century, it was also known as chessylite, after the type locality at Chessy-les-Mines near Lyon, France. [3] The mineral, a basic carbonate with the chemical formula Cu3(CO3)2(OH)2, has been known since ancient times, and was mentioned in Pliny the Elder's Natural History under the Greek name kuanos (κυανός: "deep blue," root of English cyan) and the Latin name caeruleum . [5] Copper (Cu2+) gives it its blue color. [6]

Contents

Mineralogy

Chemical structure of azurite. Color code: red = O, green = Cu, gray = C, white = H) Azurite crystal structure.jpg
Chemical structure of azurite. Color code: red = O, green = Cu, gray = C, white = H)

Azurite has the formula Cu3(CO3)2(OH)2, with the copper(II) cations linked to two different anions, carbonate and hydroxide. It is one of two relatively common basic copper(II) carbonate minerals, the other being bright green malachite. Aurichalcite is a rare basic carbonate of copper and zinc. [7] Simple copper carbonate (CuCO3) is not known to exist in nature, due to the high affinity of the Cu2+
 ion for the hydroxide anion HO−
. [8]

Azurite crystallizes in the monoclinic system. [9] Large crystals are dark blue, often prismatic. [3] [4] [7] Azurite specimens can be massive to nodular or can occur as drusy crystals lining a cavity. [10]

Azurite has a Mohs hardness of 3.5 to 4. The specific gravity of azurite is 3.7 to 3.9. Characteristic of a carbonate, specimens effervesce upon treatment with hydrochloric acid. The combination of deep blue color and effervescence when moistened with hydrochloric acid are identifying characteristics of the mineral. [7] [10]

Color

The optical properties (color, intensity) of minerals such as azurite and malachite are characteristic of copper(II). Many coordination complexes of copper(II) exhibit similar colors. According to crystal field theory, the color results from low energy d-d transitions associated with the d9 metal center. [11] [12]

Weathering

Azurite is unstable in open air compared to malachite, and often is pseudomorphically replaced by malachite. This weathering process involves the replacement of some of the carbon dioxide (CO2) units with water (H2O), changing the carbonate:hydroxide ratio of azurite from 1:1 to the 1:2 ratio of malachite: [7]

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 quite stable under ordinary storage conditions, so that specimens retain their deep blue color for long periods of time. [13]

Occurrences

Azurite from Burra Mine, South Australia Azurite, Burra Mine, South Australia.jpg
Azurite from Burra Mine, South Australia

Azurite is found in the same geologic settings as its sister mineral, malachite, though it is usually less abundant. Both minerals occur widely as supergene copper minerals, formed in the oxidized zone of copper ore deposits. Here they are associated with cuprite, native copper, and various iron oxide minerals. [7]

Fine specimens can be found at many locations. Among the best specimens are found at Bisbee, Arizona, and nearby locations, and have included clusters of crystals several inches long and spherical aggregates and rosettes up to 2 inches (51 mm) in diameter. Similar rosettes are found at Chessy, Rhône, France. The best crystals, up to 10 inches (250 mm) in length, are found at Tsumeb, Namibia. Other notable occurrences are in Utah; Mexico; the Ural and Altai Mountains; Sardinia; Laurion, Greece; Wallaroo, South Australia; Brazil and Broken Hill. [10]

Uses

Pigments

Azurite is unstable in air, however it was used as a blue pigment in antiquity. [14] Azurite is naturally occurring in Sinai and the Eastern Desert of Egypt. It was reported by F. C. J. Spurrell (1895) in the following examples; a shell used as a pallet in a Fourth Dynasty (2613 to 2494 BCE) context in Meidum, a cloth over the face of a Fifth Dynasty (2494 to 2345 BCE) mummy also at Meidum and a number of Eighteenth Dynasty (1543–1292 BCE) wall paintings. [15] 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, Armenian stone, and azurro della Magna (blue from Germany in 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, though verditer 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. 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. Lapis lazuli (the pigment ultramarine) was chiefly supplied from Afghanistan during the Middle Ages, whereas 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. [16]

Heating can be used to distinguish azurite from purified natural ultramarine blue, a more expensive but more stable blue pigment, as described by Cennino D'Andrea Cennini. Ultramarine withstands heat, whereas azurite converts to black copper oxide. [17] However, gentle heating of azurite produces a deep blue pigment used in Japanese painting techniques. [18]

Azurite pigment can be synthesized by precipitating copper(II) hydroxide from a solution of copper(II) chloride with lime (calcium hydroxide) and treating the precipitate with a concentrated solution of potassium carbonate and lime. This pigment is likely to contain traces of basic copper(II) chlorides. [19]

Jewelry

Azurite is used occasionally as beads and as jewelry, and also as an ornamental stone. [20] However, its softness and tendency to lose its deep blue color as it weathers leaves it with fewer uses. [21] 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. The notion that specimens must be carefully protected from bright light, heat, and open air to retain their intensity of color over time may be an urban legend. Paul E. Desautels, former curator of gems and minerals at the Smithsonian Institution, has written that azurite is stable under ordinary storage conditions. [13]

Prospecting

While not a major ore of copper itself, the presence of azurite is a good surface indicator of the presence of weathered copper sulfide ores. It is usually found in association with the chemically similar malachite, producing a striking color combination of deep blue and bright green that is strongly indicative of the presence of copper ores. [7]

History

Azurite was known in the pre-classical ancient world. It was used in ancient Egypt as a pigment, obtained from mines in Sinai. Ancient Mesopotamian writers report the use of a special mortar and pestle for grinding it. It was also used in ancient Greece, for example on the Acropolis in Athens. It does not appear to have been used in ancient Roman wall paintings but Roman writers certainly knew about its use as a pigment. [22] The fusing of glass and azurite was developed in ancient Mesopotamia. [23]

See also

Related Research Articles

<span class="mw-page-title-main">Lazurite</span> Alumino-silicate mineral whose blue colour is due to a sulfide species and not copper

Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]. It is a feldspathoid and a member of the sodalite group. Lazurite crystallizes in the isometric system although well‐formed crystals are rare. It is usually massive and forms the bulk of the gemstone lapis lazuli.

<span class="mw-page-title-main">Basic copper carbonate</span> Chemical compound

Basic copper carbonate is a chemical compound, more properly called copper(II) carbonate hydroxide. It is an ionic compound consisting of the ions copper(II) Cu2+
, carbonate CO2−
3, and hydroxide OH−
.

<span class="mw-page-title-main">Malachite</span> Mineral variety of copper carbonate

Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and deep, underground spaces, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare, but occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.

<span class="mw-page-title-main">Chalcanthite</span> Sulfate mineral

Chalcanthite (from Ancient Greek χάλκανθον (khálkanthon), from χαλκός (khalkós) 'copper', and ἄνθος (ánthos) 'flower, bloom') is a richly colored blue-green water-soluble sulfate mineral CuSO4·5H2O. It is commonly found in the late-stage oxidation zones of copper deposits. Due to its ready solubility, chalcanthite is more common in arid regions.

<span class="mw-page-title-main">Smithsonite</span> Mineral of zinc carbonate

Smithsonite, also known as zinc spar, is the mineral form of zinc carbonate (ZnCO3). Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in appearance and the term calamine has been used for both, leading to some confusion. The distinct mineral smithsonite was named in 1832 by François Sulpice Beudant in honor of English chemist and mineralogist James Smithson (c. 1765–1829), who first identified the mineral in 1802.

<span class="mw-page-title-main">Aurichalcite</span> Basic carbonate of zinc and copper

Aurichalcite is a carbonate mineral, usually found as a secondary mineral in copper and zinc deposits. Its chemical formula is (Zn,Cu)5(CO3)2(OH)6. The zinc to copper ratio is about 5:4. Copper (Cu2+) gives aurichalcite its green-blue colors.

<span class="mw-page-title-main">Chrysocolla</span> Phyllosilicate mineral

Chrysocolla ( KRIS-ə-KOL-ə) is a hydrous copper phyllosilicate mineral and mineraloid with the formula Cu
2 – xAl
x(H
2Si
2O
5)(OH)
4⋅nH
2O (x < 1) or (Cu, Al)
2H
2Si
2O
5(OH)
4⋅nH
2O).

Copper carbonate may refer to :

<span class="mw-page-title-main">Caledonite</span>

Caledonite, whose name derives from Caledonia, the historical name of its place of discovery (Scotland), is a richly colored blue-green sulfate-carbonate mineral of lead and copper with an orthorhombic crystal structure. It is an uncommon mineral found in the oxidized zones of copper-lead deposits.

<span class="mw-page-title-main">Brochantite</span> Copper sulfate mineral

Brochantite is a sulfate mineral, one of a number of cupric sulfates. Its chemical formula is Cu4SO4(OH)6. Formed in arid climates or in rapidly oxidizing copper sulfide deposits, it was named by Armand Lévy for his fellow Frenchman, geologist and mineralogist A. J. M. Brochant de Villiers.

<span class="mw-page-title-main">Copper(II) hydroxide</span> Hydroxide of copper

Copper(II) hydroxide is the hydroxide of copper with the chemical formula of Cu(OH)2. It is a pale greenish blue or bluish green solid. Some forms of copper(II) hydroxide are sold as "stabilized" copper(II) hydroxide, although they likely consist of a mixture of copper(II) carbonate and hydroxide. Cupric hydroxide is a strong base, although its low solubility in water makes this hard to observe directly.

Bice, from the French bis, originally meaning dark-coloured, is a green or blue pigment. In French the terms vert bis and azur bis mean dark green and dark blue respectively. Bice pigments were generally prepared from basic copper carbonates, but sometimes ultramarine or other pigments were used.

In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene-hypogene boundary. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite (Cu2S), covellite (CuS), digenite (Cu18S10), and djurleite (Cu31S16) are deposited by the descending surface waters.

<span class="mw-page-title-main">Pseudomalachite</span>

Pseudomalachite is a phosphate of copper with hydroxyl, named from the Greek for "false" and "malachite", because of its similarity in appearance to the carbonate mineral malachite, Cu2(CO3)(OH)2. Both are green coloured secondary minerals found in oxidised zones of copper deposits, often associated with each other. Pseudomalachite is polymorphous with reichenbachite and ludjibaite. It was discovered in 1813. Prior to 1950 it was thought that dihydrite, lunnite, ehlite, tagilite and prasin were separate mineral species, but Berry analysed specimens labelled with these names from several museums, and found that they were in fact pseudomalachite. The old names are no longer recognised by the IMA.

<span class="mw-page-title-main">Copper(II) carbonate</span> Chemical compound

Copper(II) carbonate or cupric carbonate is a chemical compound with formula CuCO
3. At ambient temperatures, it is an ionic solid consisting of copper(II) cations Cu2+
 and carbonate anions CO2−
3.

<span class="mw-page-title-main">Chalconatronite</span>

Chalconatronite is a carbonate mineral and rare secondary copper mineral that contains copper, sodium, carbon, oxygen, and hydrogen, its chemical formula is Na2Cu(CO3)2•3(H2O). Chalconatronite is partially soluble in water, and only decomposes, although chalconatronite is soluble while cold, in dilute acids. The name comes from the mineral's compounds, copper ("chalcos" in Greek) and natron, naturally forming sodium carbonate. The mineral is thought to be formed by water carrying alkali carbonates (possibly from soil) reacting with bronze. Similar minerals include malachite, azurite, and other copper carbonates. Chalconatronite has also been found and recorded in Australia, Germany, and Colorado.

<span class="mw-page-title-main">Blue pigments</span>

Blue pigments are natural or synthetic materials, usually made from minerals and insoluble with water, used to make the blue colors in painting and other arts. The raw material of the earliest blue pigment was lapis lazuli from mines in Afghanistan, that was refined into the pigment ultramarine. Since the late 18th and 19th century, blue pigments are largely synthetic, manufactured in laboratories and factories.

<span class="mw-page-title-main">Green pigments</span> Substances reflecting light between 475-590 nm

Green pigments are the materials used to create the green colors seen in painting and the other arts. Most come from minerals, particularly those containing compounds of copper. Green pigments reflect the green portions of the spectrum of visible light, and absorb the others. Important green pigments in art history include Malachite and Verdigris, found in tomb paintings in Ancient Egypt, and the Green earth pigments popular in the Middle Ages. More recent greens, such as Cobalt Green, are largely synthetic, made in laboratories and factories.

<span class="mw-page-title-main">Azurite (pigment)</span> Blue pigment commonly used in the Middle Ages and Renaissance

Azurite is an inorganic pigment derived from the mineral of the same name. It was likely used by artists as early as the Fourth Dynasty in Egypt, but it was less frequently employed than synthetically produced copper pigments such as Egyptian Blue. In the Middle Ages and Renaissance, it was the most prevalent blue pigment in European paintings, appearing more commonly than the more expensive ultramarine. Azurite's derivation from copper mines tends to give it a greenish hue, in contrast with the more violet tone of ultramarine. Azurite is also less stable than ultramarine, and notable paintings such as Michelangelo's The Entombment have seen their azure blues turn to olive green in time. Azurite pigment typically includes traces of malachite and cuprite; both minerals are found alongside azurite in nature, and they may account for some of the green discoloration of the pigment. The particle size of azurite pigment has been shown to have a significant effect on its chromatic intensity, and the manner of grinding and preparing the pigment therefore has a major impact on its appearance.

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. ↑ Handbook of Mineralogy
  3. 1 2 3 Mindat.org
  4. 1 2 Webmineral.com Webmineral Data
  5. ↑ The Ancient Library: Smith, Dictionary of Greek and Roman Antiquities, p.321, right col., under BLUE Archived December 20, 2005, at the Wayback Machine
  6. ↑ "Minerals Colored by Metal Ions". minerals.gps.caltech.edu. Retrieved 2023-03-01.
  7. 1 2 3 4 5 6 Klein, Cornelis; Hurlbut, Cornelius S. Jr. (1993). Manual of mineralogy : (after James D. Dana) (21st ed.). New York: Wiley. pp. 417–418. ISBN   047157452X.
  8. ↑ Ahmad, Zaki (2006). Principles of Corrosion Engineering and Corrosion Control. Oxford: Butterworth-Heinemann. pp. 120–270. ISBN   9780750659246.
  9. ↑ Zigan, F.; Schuster, H.D. (1972). "Verfeinerung der Struktur von Azurit, Cu3(OH)2(CO3)2, durch Neutronenbeugung". Zeitschrift für Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie. 135 (5–6): 416–436. Bibcode:1972ZK....135..416Z. doi:10.1524/zkri.1972.135.5-6.416. S2CID   95738208.
  10. 1 2 3 Sinkankas, John (1964). Mineralogy for amateurs. Princeton, N.J.: Van Nostrand. pp. 379–381. ISBN   0442276249.
  11. ↑ Nassau, K. (1978). "The origins of color in minerals". American Mineralogist. 63 (3–4): 219–229.
  12. ↑ Klein & Hurlbut 1993, pp. 260–263.
  13. 1 2 Desautels, Paul E. (January 1991). "Some Thoughts about Azurite". Rocks & Minerals. 66 (1): 14–23. doi:10.1080/00357529.1991.11761595.
  14. ↑ Gettens, R.J. and Fitzhugh, E.W., Azurite and Blue Verditer, in Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 2: A. Roy (Ed.) Oxford University Press 1993, p. 23–24
  15. ↑ Nicholson, Paul; Shaw, Ian (2000). Ancient Egyptian Materials and Technology. Cambridge University Press. ISBN   978-0521452571.
  16. ↑ Andersen, Frank J. Riches of the Earth. W.H. Smith Publishers, New York, 1981, ISBN   0-8317-7739-7
  17. ↑ Muller, Norman E. (January 1978). "Three Methods of Modelling the Virgin's Mantle in Early Itallan Painting". Journal of the American Institute for Conservation. 17 (2): 10–18. doi:10.1179/019713678806029166.
  18. ↑ Nishio, Yoshiyuki (January 1987). "Pigments Used in Japanese Paintings". The Paper Conservator. 11 (1): 39–45. doi:10.1080/03094227.1987.9638544.
  19. ↑ Orna, Mary Virginia; Low, Manfred J. D.; Baer, Norbert S. (May 1980). "Synthetic Blue Pigments: Ninth to Sixteenth Centuries. I. Literature". Studies in Conservation. 25 (2): 53. doi:10.2307/1505860. JSTOR   1505860.
  20. ↑ Mueller, Wolfgang (31 January 2012). "Arizona Gemstones". Rocks & Minerals. 87 (1): 64–70. doi:10.1080/00357529.2012.636241. ISSN   0035-7529. S2CID   219714562.
  21. ↑ Schumann, Walter (2009). Gemstones of the world (4th, newly rev. & expanded ed.). New York: Sterling. ISBN   9781402768293 . Retrieved 18 September 2021.
  22. ↑ Robert James Forbes, Studies in Ancient Technology, vol. 1, p. 216, Leiden: E. J. Brill, 1955 OCLC   312267983.
  23. ↑ Emmerich Paszthory, "Electricity generation or magic? The analysis of an unusual group of finds from Mesopotamia", p. 34 in, Stuart J. Fleming, Helen R. Schenck, History of Technology: The Role of Metals, University of Pennsylvania Museum of Archaeology, 1989 ISBN   0924171952.
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