Is willemite fluorescent?
Is willemite fluorescent? Yes: typically strongly, yellow-green to yellow-orange under SW and LW UV, and may be phosphorescent. 163 database records checked.
Yes. The Handbook of Mineralogy calls willemite, Zn2(SiO4), “typically strongly fluorescent in yellow-green to yellow-orange under SW and LW UV” and says it may be phosphorescent. Of 163 willemite records in the Fluorescent Mineral Society database, 161 glow under shortwave and 36 under longwave; outside New Jersey, 18 of 86 shortwave records glow blue, white or yellow, not green.
In short
- The verdict, from the sheet. The Handbook of Mineralogy willemite sheet reads: “Typically strongly fluorescent in yellow-green to yellow-orange under SW and LW UV; may be phosphorescent.” Typically, not always. The September 2026 IMA-CNMNC Master List writes willemite Zn2(SiO4), status G, 1830, Belgium; the sheet gives hardness 5.5, density 3.89 to 4.19, streak white.
- The off-Franklin check. The FMS Fluorescent Mineral Database willemite list linked 163 records on 14 November 2026; a script read each one’s luminescence summary. 75 are from Franklin or Sterling Hill, New Jersey, and every one records willemite green under shortwave. Of the 86 shortwave records from elsewhere, 68 say green and 18 say only blue, white or yellow: Tsumeb, Puttapa, the Red Cloud mine and others.
- Shortwave, mostly. 161 of 163 records give a shortwave response, 36 a longwave one and 26 a midwave one; 121 give shortwave alone. The sheet names both SW and LW; longwave lines in the records are green (20), yellow (15) or blue (1). A missing longwave line is not a tested negative, so this counts what contributors reported, not what willemite cannot do.
- Is willemite phosphorescent? The sheet says it may be. 36 of the 163 records carry an afterglow line, 8 of 75 from New Jersey and 28 of 88 from elsewhere. Modreski (1987), New Mexico Geology 9 calls “the common phosphorescence of willemite” a way to tell it from green-fluorescing uraniferous opal, which he says is almost never phosphorescent. UV lamp exposure is covered by the ICNIRP 2004 guidelines on ultraviolet exposure; this page is not safety advice.
- Colour, ore and uses. In daylight the sheet gives colourless to white, grey, flesh-red, dark brown, honey-yellow, apple-green or blue. It calls willemite “locally an important ore of zinc”; worked, Zn2SiO4 is 58.68% zinc. The sheet names no other use. Radioactivity questions go to is my mineral radioactive: the formula holds no uranium, thorium or potassium.
| Group | Records | Shortwave response | Shortwave green | Shortwave blue, white or yellow, no green | Longwave response | Midwave response | Afterglow line |
|---|---|---|---|---|---|---|---|
| Franklin and Sterling Hill, New Jersey | 75 | 75 | 75 | 0 | 19 | 11 | 8 |
| All other localities | 88 | 86 | 68 | 18 | 17 | 15 | 28 |
| All records | 163 | 161 | 143 | 18 | 36 | 26 | 36 |
| Shortwave colours, all lines | — | green 143, blue 14, white 10, yellow 1 | — | — | green 20, yellow 15, blue 1 | green 13, yellow 13 | mostly green after shortwave (30 lines) |
| Handbook sheet, as printed | — | “SW and LW UV” | “yellow-green to yellow-orange” | not in the sheet’s range | “SW and LW UV” | not named | “may be phosphorescent” |
Does willemite glow under UV? What the sheet says
Yes, typically and strongly. The Handbook of Mineralogy willemite sheet prints, after hardness 5.5 and density 3.89 to 4.19: “Typically strongly fluorescent in yellow-green to yellow-orange under SW and LW UV; may be phosphorescent.” The sheet is set in a font that pdftotext renders as “°uorescent”; a ligature-aware search, matching any glyph followed by “uoresc”, finds it. Two bands, two colours, a qualifier and a second effect.
Read against the other sheets. The comparison of how sheets word fluorescence, band by band, is on the willemite species page, and the zinc-suite qualifier ledger on is hydrozincite fluorescent; neither is repeated here. The live species page’s figures (Zn2SiO4, hardness 5.5, density 3.89 to 4.19, crystals to 10 cm) are the sheet’s, and agree with this page.
Why it glows, in one fetched source. Modreski (1987), New Mexico Geology 9 photographed willemite with calcite from Iron Mountain, Sierra County, New Mexico, under shortwave: “willemite fluoresces green, calcite fluoresces red”, with Mn2+ as the activator in both, the colours differing because Mn2+ sits in four-fold coordination in willemite and six-fold in calcite. That is his statement about his specimens; the calcite side is on is calcite UV reactive.
Is all willemite green under UV? The off-Franklin check
Method. The FMS Fluorescent Mineral Database willemite list linked 163 specimen records on 14 November 2026. Each was saved and read by script: the willemite block of its “Summary of luminescence responses”, band by band, and its locality field, grouped as New Jersey (Franklin or Sterling Hill) or elsewhere. The database is a gallery to which members submit fluorescent specimens, so every record glows: it can show which colours and bands occur, not what share of willemite fluoresces.
Result. 75 records are from Franklin or Sterling Hill, and all 75 record willemite green under shortwave. 88 are from elsewhere; 86 give a shortwave response, 68 green and 18 blue, white or yellow with no green. The 18 come from Puttapa and the Beltana mine in South Australia, the Red Cloud and Mammoth-St. Anthony mines and others in Arizona, Tsumeb and Berg Aukas in Namibia, Mfouati and Mindouli in the Republic of the Congo, and single records from Portugal and France.
Documented failure: “green means willemite”. It holds for every New Jersey record and fails for 18 of the 86 shortwave records from elsewhere, and blue and white are outside the sheet’s “yellow-green to yellow-orange”. Green is not unique to willemite either: Modreski names green-fluorescing uraniferous opal, and is hydrozincite fluorescent shows other zinc minerals glowing blue. Colour suggests; hardness 5.5, the white streak and the label decide.
Is willemite phosphorescent?
It may be, on the sheet. The line ends “may be phosphorescent”: an afterglow when the lamp goes off, possible but not promised. In the FMS records, 36 of 163 carry an afterglow line; of the afterglow lines, 30 are green after shortwave and the rest yellow, white or blue, some after longwave or midwave.
A locality pattern the records show. Only 8 of the 75 New Jersey records carry an afterglow line, against 28 of the 88 from elsewhere. That is a statement about what contributors entered, not a measurement; a contributor who did not look for an afterglow would not record one. It does mean a New Jersey piece that does not phosphoresce is in good company.
Why it matters in the field. Modreski (1987), New Mexico Geology 9 writes that “the common phosphorescence of willemite” helps distinguish it from green-fluorescent uraniferous opal, which is found on fracture surfaces in many rocks and “is almost never phosphorescent”. That opal carries uranium, so any radioactivity question goes to is my mineral radioactive; this page is not safety advice.
Shortwave or longwave for willemite?
Both, on the sheet; shortwave, overwhelmingly, in the records. 161 of 163 FMS records give a shortwave response and 121 give nothing else. 36 give longwave, green on 20 lines and yellow on 15, and 26 midwave. New Jersey and elsewhere are alike here: 19 of 75 and 17 of 88 records name longwave. Choosing a lamp is covered on best UV lamp for mineral collecting and the physics on fluorescent minerals explained.
Not a tested negative. The records say what a contributor saw under the lamps they used. Two records give no shortwave line at all, one green under midwave and one yellow under longwave. UV exposure limits are in the ICNIRP 2004 guidelines on ultraviolet exposure, quoted nowhere on this page; nothing here is safety advice.
Elsewhere on this site. The New Jersey district and its other fluorescent species are on Franklin and Sterling Hill; the zinc oxide found with willemite there is on zincite, and the magnetic black mineral, which records no fluorescence, on franklinite. More guides are in the collecting guides.
What colour is willemite, and what is it an ore of?
In daylight, many colours. The sheet gives “Colorless to white, gray, flesh-red, dark brown, honey-yellow, apple-green, blue; colorless in thin section”, streak white, lustre vitreous to resinous, hexagonal prismatic crystals to 10 cm, also granular, fibrous, botryoidal and massive. The two Franklin analyses carry MnO 0.12 and 8.96 wt%; recast on 4 oxygens that is 0.004 and 0.278 manganese per formula unit.
An ore of zinc, locally. “Of secondary origin, especially in zinc deposits developed in limestones; while uncommon, locally an important ore of zinc.” Worked on standard atomic weights, Zn2SiO4 is 58.68% zinc, the figure on Franklin and Sterling Hill. The sheet records no other use, and this page names none.
Where is willemite found? Distribution opens with Altenberg, near Moresnet, Belgium, then Tsumeb and Guchab, Namibia; Kabwe (Broken Hill), Zambia; large crystals at Franklin and Sterling Hill; Balmat, New York; the Mammoth-St. Anthony and Red Cloud mines, Arizona; Mont Saint-Hilaire, Quebec; and “a large deposit at the Puttapa zinc mine, near Beltana, South Australia”. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.