Willemite

Willemite is a zinc silicate mineral (Zn2SiO4) and a minor ore of zinc. It is highly fluorescent (green) under shortwave ultraviolet light. It occurs in a variety of colors in daylight, in fibrous masses, solid brown masses (troostite), and apple-green gemmy masses.

Willemite
Willemite from Namibia
General
CategorySilicate mineral
Formula
(repeating unit)		Zn2SiO4
Strunz classification9.AA.05 (10 ed)
8/A.01-20 (8 ed)
Dana classification51.1.1.2
Crystal systemTrigonal
Crystal classRhombohedral (3)
H-M symbol: (3)
Space groupR3
Identification
ColorColorless to white, gray, black, flesh-red, burgundy-red, pink, brown, dark brown, mahogany-brown, honey-yellow, yellow, apple-green, blue, pastel green, light blue, azure-blue
Crystal habitFibrous, botryoidal to massive
Cleavage{0001}, {1120} - imperfect
FractureIrregular to conchoidal
Mohs scale hardness5.5
LusterVitreous to resinous
DiaphaneityTransparent to opaque
Specific gravity3.9 – 4.2
Optical propertiesUniaxial (+)
Refractive indexnω = 1.691 – 1.694 nε = 1.719 – 1.725
Birefringenceδ = 0.028
Other characteristicsStrongly fluorescent; may be phosphorescent
References[1][2][3]

It was discovered in 1829 in the Belgian Vieille-Montagne mine. Armand Lévy was shown samples by a student at the university where he was teaching. Lévy named it after William I of the Netherlands[4] (it is occasionally spelled villemite).[5][6][7] The troostite variety is named after Dutch-American mineralogist Gerard Troost.[8]

Formation and associated minerals

Willemite is usually formed as an alteration of previously existing sphalerite ore bodies, and is usually associated with limestone. It is also found in marble and may be the result of a metamorphism of earlier hemimorphite or smithsonite.[9] Crystals have the form of hexagonal prisms terminated by rhombohedral planes: there are distinct cleavages parallel to the prism-faces and to the base. Granular and cleavage masses are of more common occurrence.[10] It occurs in many places, but is best known from Arizona and the zinc, iron, manganese deposits at Franklin and Sterling Hill Mines in New Jersey. It often occurs with red zincite (zinc oxide) and franklinite (Fe,Mn,Zn)(Fe,Mn)2O4 (an iron rich zinc mineral occurring in sharp black isometric octahedral crystals and masses). Franklinite and zincite are not fluorescent.

Uses

Artificial willemite was used as the basis of first-generation fluorescent tube phosphors. Doped with manganese-II, it fluoresces with a broad white emission band. Some versions had some of the zinc replaced with beryllium. In the 1940s it was largely replaced by the second-generation halophosphors based on the fluorapatite structure. These, in turn have been replaced by the third-generation TriPhosphors.[11][12]

Willemite variety troostite from New Jersey
Crystal structure of willemite

Photo comparison
In natural and in fluorescent light

See also

References
  1. Handbook of Mineralogy
  2. Mindat
  3. Webmineral
  4. Denayer, Julien; et al. (2017). "Les sciences géologiques à l'Université de Liège : deux siècles d'évolution Partie 1 : de la fondation à la Première Guerre Mondiale". Bulletin de la Société Royale des Sciences de Liège (in French). 86. doi:10.25518/0037-9565.7303. ISSN 0037-9565. En 1829, [Armand Lévy] décrivit la willémite [...], nouvelle espèce minérale découverte à la Vieille-Montagne à Moresnet, et la dédia à Guillaume (Willem) 1er des Pays-Bas (Lévy, 1830 ; Lacroix, 1919 ; Buttgenbach, 1947a). « Ce minéral, très-abondant à Moresnet, avait échappé à l’attention des minéralogistes qui avaient visité cette localité, lorsqu’un élève de l’université de Liége en apporta plusieurs morceaux qui me parurent appartenir à une espèce différente de celles que je connaissais ; en conséquence je me rendis sur les lieux, et, après avoir mûrement examiné les nombreux échantillons que j’y rencontrai, je fus convaincu que ma conjecture était fondée » (Lévy, 1843). (Translation: "In 1829, [Lévy] described willemite, a new mineral discovered at Moresnet's Vieille-Montagne and dedicated to William I of the Netherlands. "The mineral—quite abundant in Moresnet—went unnoticed by mineralogists who had visited this location. A student of the University of Liège brought me several pieces that I was unfamiliar with, so I went to these places. After carefully examining the many samples that I came across, I was convinced that my supposition was founded.")
  5. See:
    • Levy, A. (1830). "Lüttich, 14. September 1829". Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde (in German). 1: 71. From p. 71: "Bei einer Exkursion, welche ich neulich gemacht, glaube ich ein neues Mineral entdeckt zu haben; es soll Willemite heissen, nach S.M. dem König der Niederlande." (During an excursion which I made recently, I believe that I discovered a new mineral; it shall be called "Willemite", after His Majesty the King of the Netherlands.)
    • Chester, Albert Huntington (1896). A Dictionary of the Names of Minerals Including Their History and Etymology. New York City, New York, USA: John Wiley & Sons. p. 288.
  6. Wurtz, Charles Adolphe (1878). Dictionnaire de chimie pure et appliquée. Hachette. p. 722. Syn. Wihlemite, williamsite, troostite. [...] dans les amas de calamine de la Vieille-Montagne
  7. Bulletin de Minéralogie (in French). Masson. 1919. p. 127. Ainsi s'explique qu'en 1829 il ait dédié au roi des Pays-Bas, Wilhem I, la villemite, qu'il venait de découvrir à la Vieille-Montagne. ("[...] in 1829 he dedicated to the king of the Netherlands, William I, the villemite, which he had just discovered at Vieille-Montagne.")
  8. "troostite". Merriam-Webster Dictionary.
  9. Klein, Cornelis (2007). The Manual of Mineral Science, p.484. John Wiley and Sons, Inc., Hoboken. ISBN 9780471721574.
  10.  One or more of the preceding sentences incorporates text from a publication now in the public domain: Spencer, Leonard James (1911). "Willemite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. 28 (11th ed.). Cambridge University Press. p. 658.
  11. Thayer, R. N. "The Fluorescent Lamp: Early U. S. Development".
  12. Kane, Raymond; Sell, Heinz (2001). "A Review of Early Inorganic Phosphors". Revolution in lamps: a chronicle of 50 years of progress. p. 98. ISBN 978-0-88173-378-5.
  • Media related to Willemite at Wikimedia Commons
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