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Azurite

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Azurite is a member of carbonate minerals with chemical composition of carbonate hydroxide, formula: Cu3(CO3)2(OH)2.  Its characteristic properties deep blue to violet-blue color. Azurite was used as a blue pigment in 15th- to 17th-century European art and probably in the production of blue glaze in ancient Egypt. It takes its name from the Persian word lazhuward, which means “blue.” Azurite forms either tabular or prismatic crystals with a wide variety of habits. Tabular crystals commonly have wedge-shaped terminations. Azurite forms rosette-shaped crystalline aggregates or occurs in massive, stalactitic, or botryoidal forms. Well-developed crystals are dark azure blue in color, but massive or earthy aggregates may be paler. Azurite is a secondary mineral formed in the oxidized portions of copper deposits. Ancient people used it as an ore of copper, as a pigment, as a gemstone, and as an ornamental stone. It is still used for all of these purposes today

Name: From the Persian lazhward, for its characteristic blue color.

Association: Malachite, chrysocolla, brochantite, antlerite, cuprite, cerussite, smithsonite, calcite, dolomite

Mineral Group: Aragonite Group

Crystallography: Monoclinic; prismatic. Habit varied. Crystals frequently complex in habit and distorted in development. Also in radiating spherical groups.

Composition: A basic carbonate of copper, Cu3(C03)2(0H )2. CuO = 69.2 per cent, C02 = 25.6 per cent, H20 = 5.2 per cent. Cu = 55.3 per cent.

Diagnostic Features: Characterized chiefly by its azure-blue color and effervescence in hydrochloric acid.

Rare Hydrous Carbonates: Aurichalcite, a basic carbonate of zinc and copper, pale green to blue, in monoclinic acicular crystals. GayLussite, CaC0 3-Na2C0 3 -5H20, monoclinic; trona, 3Na20-4C03-5H20, monoclinic; both found in saline lake deposits.

Chemical Properties

Chemical Classification Carbonate mineral
Formula Cu3(CO3)2(OH)2

Azurite Physical Properties

Crystal habit Massive, prismatic, stalactitic, tabular
Color Azure blue, blue, light blue, or dark blue; light blue in transmitted light
Streak Light blue
Luster Vitreous
Cleavage Perfect Perfect on {011}; on {100} fair; on {110} in traces.
Diaphaneity Transparent, Translucent
Mohs Hardness 3,5 – 4
Crystal System Monoclinic
Tenacity Brittle
Density 3.77 g/cm3 (Measured)    3.834 g/cm3 (Calculated)
Fracture Conchoidal
Parting None

Azurite Optical Properties

Color / Pleochroism Pleochroic in blue, with absorption Z greater than Y greater than X.
2V: Measured: 68° , Calculated: 64°
RI values: nα = 1.730 nβ = 1.758 nγ = 1.838
Twinning Rare, across {101}, {102} or {001}.
Optic Sign Biaxial (+)
Birefringence δ = 0.108
Relief High
Dispersion: relatively weak

Occurrence of Azurite

Azurite is a secondary mineral commonly forming when water containing carbon dioxide descends to the Earth and reacts with underground copper ores. The carbonic acid of these waters dissolves a small amount of copper from the ore. Dissolved copper is carried with water until it reaches a new geochemical environment. This new medium may be a zone where water chemistry or temperature adjustments are made or evaporation occurs. If the conditions are correct, mineral azurite probably occurs. If these conditions persist for a long time, a large accumulation of azurite is likely to increase. This has occurred in many parts of the world.

Azurite rainfall occurs in porous areas, fractures and cavities of underground rocks. The resulting azurite is normally massive or nodular. In uncommon cases, it is discovered as stalactites and botryoidal growth. Uniformly shaped monoclinic crystals are identified from time to time. they may occur if the azurite is precipitated unrestricted in a fracture or hollow area and is not then degraded using crystallization or rock motions.

Uses Area

Pigments: Azurite is not a useful pigment because it is unstable in air. It was however used as a blue pigment in antiquity. Azurite is naturally occurring in Sinai and the Eastern Desert of Egypt.

Jewelry: It 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, 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 very similar malachite, producing a striking color combination of deep blue and bright green that is strongly indicative of the presence of copper ores.

Distribution

Widespread, with many localities producing good crystals.

  • From Chessy, near Lyon, Rhone, France.
  • At Alghero and elsewhere on Sardinia, Italy.
  • In the Zmeinogorsk (Schlangenberg) and Zolotuskinskii mines, Altai Mountains, Russia. Large crystals at the Touissit mine, near Oujda, Morocco.
  • An ore at the Chingola mine, Nchanga, Zambia.
  • Extraordinary examples from Tsumeb, Namibia.
  • In the USA, in Arizona, fine examples from the Copper Queen and other mines of the Warren district, Bisbee, Cochise Co.; at Morenci, Greenlee Co.; in the Mammoth-St. Anthony mine, Pinal Co.; from the New Cornelia mine, Ajo, Pima Co.; at the Kelly and Graphic mines, Magdalena, Socorro Co., New Mexico; in Utah, in the Apex mine, St. George, Washington Co., and at the Big Indian mine, near La Sal, San Juan Co.
  • Fine crystals from the El Cobre mine, Concepcion del Oro, and at the San Carlos mine, Mazapil, Zacetecas, Mexico.
  • In Australia, many localities, as in New South Wales, at Broken Hill, also fine crystals from the Girilambone mine, north of Nyngan.
  • In China, from the Yang Chweng mine, Shilu, Guangdong Province, China.



References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
Cite this article as: Geology Science. (2019). Azurite. [online] Available at: http://geologyscience.com/minerals/azurite/ [12th November 2019 ]
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