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Mineralpedia Details for Willemite

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Willemite

Willemite

The first, and self-proclaimed, King of the Netherlands, William I, has the honor of Willemite being named for him. At the time, the type locality of Willemite was in the Netherlands. Willemite is a secondary mineral, usually in limestone-developed zinc deposits. An uncommon but important ore of zinc at some of its many widespread localities. Willemite is highly fluorescent as a yellow-green to –orange under both short-wave and long-wave ultraviolet light and may also be phosphorescent.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/willemite.pdf

Formula
Zn2SiO4 
Crystal System
Trigonal 
Crystal Habit
Prismatic, Massive - Granular, Massive 
Cleavage
Poor, Poor, None 
Luster
Vitreous - Resinous 
Color
white, yellow, green, reddish brown, black 
Streak
white 
Class
Trigonal - Rhombohedral 
Fracture
Uneven 
Hardness
5.5 
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Willemite from Grootfontein, Namibia

Willemite
            from Grootfontein, Namibia

Clear, prismatic crystals to 3mm in exceptional sprays.

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Willemite from Sterling Hill mine, Ogdensburg, Sussex Co., New Jersey, United States

Willemite
            from Sterling Hill mine, Ogdensburg, Sussex Co., New Jersey, United States

A large well formed Willemite crystal to 2cm perched on a bit of Calcite-Willemite-Franklinite matrix.

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Willemite from Tsumeb mine, Tsumeb, Namibia

Willemite
            from Tsumeb mine, Tsumeb, Namibia

Light mint green Willemite crystals to 3mm as singles and groups with yellow Mimetite. Notice the light green balls are Malachite.

Reddish   brown "Trootsite" a mangansese rich variety of Willemite, which also occurs at Franklin. The Tsumeb trootsite is botryoidal however and composed of aggregates of rich reddish brown curved and balled up rhombic crystals.

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Willemite from Franklin, Sussex Co., New Jersey, United States

Willemite
            from Franklin, Sussex Co., New Jersey, United States

Excellent prismatic, striated, and clear WIllemite crystals to about 1.5mm  with other thicker and larger in a seam lined with orange, pseudorhombohedral crystals to about 0.75mm.

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Willemite from Lusaka, Lusaka Province, Zambia

Willemite
            from  Lusaka, Lusaka Province, Zambia
Special Info
Fluorescent

Colorless, acicular Willemite, which is intensely fluorescent green in open cavities with radial compact, brown crystals in the matrix. The matrix does not fluoresce, indicating it is not Willemite.

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