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Willemite, Calcite and Franklinite sample under visible and UV light (bottom)
Chemical formulaZinc silicate (Zn2SiO4)
ColorBlue to Green
Crystal systemRhombohedral
Cleavage{010}, {100} - imperfect
FractureUneven, Conchoidal
Mohs Scale hardness5.5
LusterVitreous - Resinous
Specific gravity3.9 - 4.2

Willemite is a zinc silicate (Zn2SiO4) and a minor ore of zinc. It is highly fluorescent (green) under shortwave ultraviolet light. It occurs in all different colors in daylight, in fibrous masses, solid brown masses ("troostite"), and apple green gemmy masses. Willemite is usually formed as an alteration of previously existing sphalerite ore bodies, and is usually associated with limestone. It occurs in many places, but is best known from Arizona and the world famous zinc, iron, manganese deposits at Franklin Furnace, 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.

It was discovered in 1830 and named after William I of the Netherlands.

See also


  • Mineral galleries
  • Mindat
  • Webmineral
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Willemite". A list of authors is available in Wikipedia.
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