What is Willemite?
Willemite is a zinc silicate prized for bright green, yellow or colourless crystals and for intense fluorescence in many specimens.
Mineralogy and structure
Reference formula: Zn2SiO4. Willemite is trigonal and is commonly associated with franklinite and zincite in classic New Jersey material. COD 3000242 provides an exact Zn2SiO4 structural reference. Willemite is classified with silicates and has trigonal crystal symmetry. Typical hardness is 5.5–6.5 on the Mohs scale and specific gravity is approximately 3.9–4.2.
Colour, lustre and habit
Typical colours include colourless, white, green, yellow, brown, red. The usual prismatic, granular, massive habit and vitreous, resinous, adamantine lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Willemite forms in or is associated with oxidised zinc deposits, metamorphosed zinc ores, skarns and secondary cavities. Important documented localities include New Jersey in the United States, Namibia, Belgium, Zambia, Mexico and Sweden.
The fluorescent zinc silicate collectors recognise instantly
Willemite is a proven cabinet favourite: colour in daylight, strong fluorescence under suitable UV and classic ore localities create a persuasive collecting and sales story.
Collecting and care
Protect crystals from impact and acids; disclose fluorescence and locality, and avoid confusing synthetic or treated material with natural willemite.
