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 and apple-green gemmy masses. Troostite is a variant in which part of the zinc is partly replaced by manganese, it occurs in solid brown masses.
| Willemite | |
|---|---|
Willemite from Namibia | |
| General | |
| Category | Silicate mineral |
| Formula (repeating unit) | Zn2SiO4 |
| IMA symbol | Wlm |
| Strunz classification | 9.AA.05 (10 ed) 8/A.01-20 (8 ed) |
| Dana classification | 51.1.1.2 |
| Crystal system | Trigonal |
| Crystal class | Rhombohedral (3) (same H-M symbol) |
| Space group | R3 |
| Identification | |
| Color | Colorless 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 habit | Fibrous, botryoidal to massive |
| Cleavage | {0001}, {1120} – imperfect |
| Fracture | Irregular to conchoidal |
| Mohs scale hardness | 5.5 |
| Luster | Vitreous to resinous |
| Diaphaneity | Transparent to opaque |
| Specific gravity | 3.9 – 4.2 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.691 – 1.694 nε = 1.719 – 1.725 |
| Birefringence | δ = 0.028 |
| Other characteristics | Strongly fluorescent; may be phosphorescent |
| References | |
| Major varieties | |
| troostite | zinc is partly replaced by manganese |
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 (it is occasionally spelled villemite). The troostite variety is named after Dutch-American mineralogist Gerard Troost.
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