Franklinite, zincite and willemite are all rare zinc minerals that are found at one distinct location in Franklin, New Jersey. This sample shows the dark frankl — Photo: Nessa Eull · CC0
Willemite
Also known as: Troostite (brown var.).
Zinc silicate — the famous 'fluorescent green' mineral of Franklin, New Jersey.
Intro adapted from Wikipedia (CC BY-SA).
Willemite is an IMA-recognized mineral species in the silicate class, with the chemical formula Zn₂SiO₄.
It crystallizes in the hexagonal crystal system (space group R-3). It is a member of the Phenakite structural group.
Key properties: Mohs hardness 5.5; specific gravity 3.89–4.19; typically green or yellow or brown or blue or colorless or red or white; White streak; Vitreous to resinous luster; refractive index 1.707; optically uniaxial.
IMA symbol Wlm, grandfathered status — known before the IMA’s founding, named in 1830.
Of secondary origin, especially in zinc deposits developed in limestones; while uncommon, locally an important ore of zinc.
It is found associated with Nasonite, glaucochroite, leucophoenicite (Franklin, New Jersey, USA); malachite, mimetite, rosasite, duftite, cerussite (Tsumeb, Namibia).
The name refers to William I (1772–1843), King of the Netherlands (1815–1840).
Collections: Collector Favorites, Fluorescent & Glowing.