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www.mineralgallery.co.za Minerals U-Z |
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Willemite |
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Name
Willemite
Chemistry
Zn2SiO4 Zinc silicate
Uses
As a minor ore of zinc and as a mineral specimen
Color
Green to colorless
Hardness
5.5
Specific gravity
3.9-4.2
Crystals
The crystals are prismatic but are usually found as massive or granular ore.
Accompanied by:
Smithsonite and dolomite.
Fracture
Uneven
Luster
Vitreous to resinous
Cleavage
Basal, it cleaves well
Streak
White
Similar to:
Smithsonite
Willemite is usually distinguished by it's greenish color but it may vary from near white to brown. It is usually strongly fluorescent.
Willemite occurs in the oxidized zone of zinc ore deposits, but never in large amounts. It is named in honor of King William I (Willem Frederik) of the Netherlands.
Willemite at Tsumeb
Willemite was found early in Tsumeb, but was not recognized as such. A specimen from around 1915 contains small willemite crystals forming a perimorph after mimetite. This mineral is known in varying colors and forms from Tsumeb. White bundles of needles are the most common habit. The finest specimen which made Tsumeb a world-class locality for willemite, are gemmy, blue crystals up to 1 cm on white calcite. Nearly as attractive are lemon-yellow, hexagonal gemmy crystals up to 1 cm which are associated with pale blue balls of of rosasite or with green adamite. These specimens were found on the deepest levels, from 43 to 46 levels. Willemite was relatively abundant for a short period during the 70's. The other day I met an old timer miner who were involved in the taking out of this batch. He sold the bulk to Sid Peters from Windhoek and lost his job because of it.
Willemite is often described as an unknown mineral because of it's varying appearance and associations with other minerals. It can be distinguished by the five-sided pinacoid and the glassy luster, but, unlike other occurrences, Tsumeb willemite is not fluorescent under ultraviolet radiation.
