Vanadinite

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Vanadinite
Specific gravity
6.8–7.1 (measured) 6.95 (calculated)
Optical propertiesUniaxial (−)
Refractive indexnω = 2.416, nε = 2.350
Birefringenceδ = 0.066
Ultraviolet fluorescenceNone
Melting point3,470 °F (1,910 °C)
References[2][3][4]

Vanadinite is a

phosphates, with the chemical formula Pb5(VO4)3Cl. It is one of the main industrial ores of the metal vanadium and a minor source of lead. A dense, brittle mineral, it is usually found in the form of red hexagonal crystals. It is an uncommon mineral, formed by the oxidation of lead ore deposits such as galena. First discovered in 1801 in Mexico
, vanadinite deposits have since been unearthed in South America, Europe, Africa, and North America.

Origins

Vanadinite is an uncommon mineral, only occurring as the result of chemical alterations to a pre-existing material. It is therefore known as a secondary mineral. It is found in

barite.[3][5]

It was originally discovered in Mexico by the Spanish mineralogist Andrés Manuel del Río in 1801. He called the mineral "brown lead" and asserted that it contained a new element, which he first named pancromium and later, erythronium. However, he was later led to believe that this was not a new element but merely an impure form of chromium. In 1830, Nils Gabriel Sefström discovered a new element, which he named vanadium. It was later revealed that this was identical to the metal discovered earlier by Andrés Manuel del Río. Del Río's "brown lead" was also rediscovered, in 1838 in Zimapan, Hidalgo, Mexico, and was named vanadinite because of its high vanadium content. Other names that have since been given to vanadinite are johnstonite and lead vanadate.[6]

Occurrence

Vanadinite occurs as a secondary mineral in the

barite, and various iron oxide minerals.[4]

Deposits of vanadinite are found worldwide including Austria, Spain, Scotland, the Ural Mountains, South Africa, Namibia, Morocco, Argentina, Mexico, and four states of the United States: Arizona, Colorado, New Mexico, and South Dakota.[3][5][7]

Vanadinite deposits are found in over 400 mines across the world. Notable vanadinite mines include those at Mibladen and Touisset in Morocco; Tsumeb, Namibia; Cordoba, Argentina; and Sierra County, New Mexico, and Gila County, Arizona, in the United States.[8]

Structure

Vanadinite is a lead chlorovanadate with the chemical formula Pb5(VO4)3Cl. It is composed (by weight) of 73.15% lead, 10.79% vanadium, 13.56% oxygen, and 2.50% chlorine. Each structural unit of vanadinite contains a chlorine ion surrounded by six

divalent lead ions at the corners of a regular octahedron, with one of the lead ions provided by an adjoining vanadinite molecule. The distance between each lead and chlorine ion is 317 picometres. The shortest distance between each lead ion is 4.48 Å. The octahedron shares two of its opposite faces with that of neighbouring vanadinite units, forming a continuous chain of octahedrons. Each vanadium atom is surrounded by four oxygen atoms at the corners of an irregular tetrahedron. The distance between each oxygen and vanadium atom is either 1.72 or 1.76 Å. Three oxygen tetrahedrons adjoin each of the lead octahedrons along the chain.[2][9][10]

Crystal packing
Chloride coordination sphere
Lead #1 coordination sphere
Lead #2 coordination sphere
Vanadium coordination sphere

Crystals of vanadinite conform to a

Å and c = 7.343 Å, where a is the length of each side of the hexagon and c is the height of the prism. The volume of each unit cell of vanadinite, given by the formula V = a2c sin(60°), is 678.72 Å3.[2][5]

Characteristics

Vanadinite is in the

isomorphic substitute for vanadium (in the first two cases) or lead (in the second). Vanadinite when containing a high amount of the arsenic impurity is known as endlichite.[3][5]

Vanadinite is usually bright-red or orange-red in colour, although sometimes brown, red-brown, grey, yellow, or colourless. Its distinctive colour makes it popular among mineral collectors. Its

anisotropic, meaning that some of its properties differ when measured along different axes. When measured perpendicular and parallel to its axis of anisotropy, its refractive indices are 2.350 and 2.416 respectively. This gives it a birefringence of 0.066.[2][3][5]

Vanadinite is very brittle, producing small,

specific gravity can range between 6.6 and 7.2 because of impurities.[3][5][7]

Uses

Along with

vanadium pentoxide (V2O5). Reduction of vanadium pentoxide with calcium gives pure vanadium.[11]

Image gallery

  • Vanadinite in hexagonal shaped crystals
    Vanadinite in
    hexagonal
    shaped crystals
  • Vanadinite that does not show the characteristic red colour
    Vanadinite that does not show the characteristic red colour
  • A pile of thousands of crystals, showing their hexagonal shape
    A pile of thousands of crystals, showing their hexagonal shape
  • Vanadinite on barite, from Mibladene, Upper Moulouya lead district, Midelt, Drâa-Tafilalet Region, Morocco
    Vanadinite on barite, from Mibladene, Upper Moulouya lead district, Midelt, Drâa-Tafilalet Region, Morocco
  • Crystals of vanadinite (var. endlichite), from Touissit, Touissit District, Oujda-Angad Province, Oriental Region, Morocco
    Crystals of vanadinite (var. endlichite), from Touissit, Touissit District, Oujda-Angad Province, Oriental Region, Morocco
  • Crystals of vanadinite and siderite, from Taouz Er Rachidia Province, Drâa-Tafilalet Region, Morocco
    Crystals of vanadinite and siderite, from Taouz Er Rachidia Province, Drâa-Tafilalet Region, Morocco

See also

References

Wikimedia Commons has media related to Vanadinite.
  1. S2CID 235729616
    .
  2. ^ a b c d "Vanadinite Mineral Data". WebMineral.com. Retrieved 9 June 2007.
  3. ^ a b c d e f "Vanadinite". MinDat.org. Retrieved 9 June 2007.
  4. ^
    ISBN 0962209732
    .
  5. ^ a b c d e f Treasures of the Earth: The Minerals and Gemstone Collection – Vanadinite factsheet. Orbis Publishing Ltd. 1995.
  6. S2CID 197594307
    .
  7. ^ a b Spencer, Leonard James (1911). "Vanadinite" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 27 (11th ed.). Cambridge University Press.
  8. ^ "Vanadinite". Minerals.net. Retrieved 26 June 2007.
  9. ^ J. Trotter & W. H. Barnes (1958). "The Structure of Vanadinite" (PDF). The Canadian Mineralogist. Retrieved 26 June 2007.
  10. ^ Dai, Yongshan; Hughes, John M. (1989). "Crystal structure refinements of vanadinite and pyromorphite" (PDF). Can. Mineral. 27 (2): 189–192.
  11. ^ Donal O'Leary (2000). "Vanadium". University College Cork. Archived from the original on 5 February 2017. Retrieved 26 June 2007.
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