Mineralpedia Details for Willemite

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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
WebMineral: View Willemite
Mindat: View Willemite

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

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

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.

Red to orange barrel-shaped and hexagonal prismatic crystals from 1 to 2mm composing the entire specimen. The specimen has been tested by XRD. Even the bluish botryoidal mass in the last few photos is Willemite.

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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.

Lime green crystalline Willemite. Acquired by Hampson in 1945. Intense green fluorescence.

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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.