Is sphalerite UV reactive?
Sometimes. The Handbook lists sphalerite, zinc sulphide, hardness 3.5 to 4, as fluorescent with no colour or band; IGS gives orange-red to red. Reading a glow.
Sometimes. The Handbook of Mineralogy sheet lists sphalerite, ZnS, hardness 3.5 to 4, as fluorescent with no colour or UV band named; the International Gem Society gives bright orange-red to red under longwave and shortwave UV, from many localities. Not every piece responds, and blue or green is not sphalerite’s recorded colour.
In short
- The sheet’s words. The Handbook of Mineralogy sphalerite sheet reads: Pyroelectric, may be triboluminescent, fluorescent. One word, no colour, no band. A ligature-aware script finds it, finds the lines on the hemimorphite and willemite sheets (the positive controls), and finds nothing on the wurtzite sheet, the other ZnS on the September 2026 IMA-CNMNC Master List.
- The colour. The International Gem Society data panel gives bright orange-red to red in LW and SW, from many localities, and says material from Otavi, Namibia is triboluminescent. That is the colour to expect if the sphalerite itself is responding.
- The glow-colour key. On a zinc-ore specimen, orange-red to red points at the sphalerite. Pale blue to lilac matches hydrozincite, which its sheet says forms at the expense of sphalerite. Pale green or pale blue matches smithsonite, bluish under SW matches hemimorphite, and yellow-green matches willemite. Hardness then decides: 3.5 to 4 for sphalerite against 2 to 2.5, 4 to 4.5, 4.5 to 5 and 5.5.
- Documented failure: the iron rule. It is tempting to say black, iron-rich sphalerite cannot glow, since Modreski 1987, New Mexico Geology 9 lists Fe2+ among quenchers. Modreski does not apply that to sphalerite: he calls it a semiconductor whose fluorescence is more difficult to attribute to a specific metal impurity. This page therefore gives no iron rule.
- Lamps and safety. Lamp choice is on best UV lamp for mineral collecting and the background on fluorescent minerals explained. Exposure limits for 180 to 400 nm are in the ICNIRP 2004 guidelines on limits of exposure to ultraviolet radiation; this page is not safety advice. The Handbook’s St Christoph analysis carries 0.28% cadmium; hazards are covered on toxic minerals in a collection, which this page does not replace.
| Colour seen | Source and wording | Band named | Mineral | Hardness | Streak | 20.00 g in water |
|---|---|---|---|---|---|---|
| Orange-red to red | IGS: bright orange-red to red in LW, SW, from many localities. Handbook: fluorescent, no colour | LW and SW (IGS); none (Handbook) | Sphalerite | 3.5 to 4 | Pale brown to pale yellow and white | 14.87 to 15.12 g |
| Pale blue to lilac | Hydrozincite sheet: fluoresces pale blue to lilac under UV; formed at the expense of sphalerite or smithsonite | None | Hydrozincite | 2 to 2.5 | Not printed | 15.00 g |
| Pale green or pale blue | Smithsonite sheet: may fluoresce pale green or pale blue under UV | None | Smithsonite | 4 to 4.5 | White | 15.49 g |
| Bluish | Hemimorphite sheet: may fluoresce bluish under SW UV | SW | Hemimorphite | 4.5 to 5 | White | 14.24 g |
| Yellow-green to yellow-orange | Willemite sheet: typically strongly fluorescent under SW and LW UV. Sterling Hill Mining Museum: thin willemite coatings cause spurious green in many other species at Franklin and Ogdensburg | SW and LW | Willemite | 5.5 | White | 14.86 to 15.23 g |
| Orange, on Franklin material | Sterling Hill Mining Museum: thin clinohedrite coatings cause a spurious orange | Not stated | Clinohedrite (coating) | — | — | — |
| Weak red to violet | Sterling Hill Mining Museum: in many cases light from the lamp reflected from the specimen | — | None (reflection) | — | — | — |
| Nothing | Wurtzite sheet: no luminescence printed | — | Wurtzite, the other ZnS | 3.5 to 4 | Brown | 15.11 g |
Does sphalerite glow under a UV lamp?
It can; the record does not say every piece does. The Handbook of Mineralogy sphalerite sheet gives sphalerite as cubic zinc sulphide, (Zn,Fe)S, hardness 3.5 to 4, density 3.9 to 4.1, streak pale brown to pale yellow and white, and its physical-properties line ends: Pyroelectric, may be triboluminescent, fluorescent. The word may stands before triboluminescent and is not repeated before fluorescent; the line names no colour and no UV band.
Method. The search tolerates the dropped or garbled fl ligature that older sheets show in pdftotext output, so it matches uoresc as well as fluoresc, plus phosphoresc, luminesc and UV, and ignores reference titles. It finds the lines on the hemimorphite and willemite sheets, the positive controls, and on the sphalerite sheet. On the wurtzite sheet, the second ZnS row on the September 2026 IMA list, it finds nothing.
The colour comes from a second source. The International Gem Society data panel gives sphalerite’s luminescence as bright orange-red to red in LW and SW, from many localities, and luminescence type as fluorescent, UV-long and UV-short. From many localities is not all localities: a dark piece under the lamp is consistent with the record, not a failed identification.
Why is sphalerite unusual among sulphides under UV?
Because most sulphides do not fluoresce at all. Modreski 1987, New Mexico Geology 9 says that most metallic or submetallic minerals, including the metallic native elements and most sulfides and sulfosalts, do not exhibit fluorescence. In the same introduction he treats sphalerite as the type example of a semiconducting sulphide: in such minerals the electronic transitions are not localized on particular atoms but are a function of the total composition, interpreted in terms of band theory.
What that rules out. Modreski adds that for semiconductors it is more difficult to attribute fluorescence to a specific metal impurity. He also lists Fe2+, Cu2+ and Ni2+ among quenchers in general. Putting those together into a rule that iron-rich, black sphalerite will not glow is a step neither source takes, so this page does not take it. That is the documented failure behind the iron rule: the tempting inference is not in the sources.
Identity first. The sheet’s name line says sphalerite was mistaken for galena. The live sphalerite page covers the streak and weight tests that separate the two; a lamp is not one of them.
How do I read a glow on a sphalerite specimen? The glow-colour key
Start with the colour, finish with hardness. The key in the table above lists, for each colour, the fetched source that records it and the mineral it records it for. Orange-red to red is the International Gem Society’s colour for sphalerite. The blue, lilac and green rows are the zinc minerals that grow in the oxidized zone of zinc deposits on their own sheets, hydrozincite, smithsonite and hemimorphite, plus willemite. The hydrozincite sheet says it forms at the expense of sphalerite or smithsonite.
Then test the glowing spot, not the specimen. Hardness separates every row: sphalerite 3.5 to 4, hydrozincite 2 to 2.5, smithsonite 4 to 4.5, hemimorphite 4.5 to 5, willemite 5.5. Heft does not: a 20.00 g piece of sphalerite reads 14.87 to 15.12 g in water, inside willemite’s 14.86 to 15.23 g and around hydrozincite’s 15.00 g. The streak on how to use a streak plate is pale on all of them.
Two rows that are not minerals responding. The Sterling Hill Mining Museum fluorescence page warns that thin coatings of clinohedrite or willemite on Franklin and Ogdensburg material give a spurious orange or green to many other species, and that much weak red to violet in the hobbyist literature is lamp light reflected from the specimen. Each sheet line here describes the species, not a particular piece. The neighbour check on is wulfenite UV reactive and the blue-zinc tests on is hydrozincite fluorescent and is hemimorphite UV reactive work the same way for other hosts.
Is Franklin sphalerite fluorescent?
The sources read here do not say. The sphalerite sheet’s Distribution field names Freiberg and Neudorf, the Lengenbach quarry, Horní Slavkov and Příbram, Rodna, the Aliva mine, Alston Moor, Dal’negorsk, Watson Lake, the Tri-State district (Baxter Springs, Joplin, Picher), the Elmwood mine, the Eagle mine at Gilman, Santa Eulalia, Naica and Cananea, and Huaron, Casapalca and Huancavelica. It does not name Franklin or Sterling Hill.
What the Franklin page says instead. The Franklin and Sterling Hill page explains what the ore was and which of its minerals the sheets record as fluorescent. A glowing spot on Franklin zinc ore is, on the museum’s own warning, first a question about willemite or clinohedrite coatings.
Lamps. Modreski describes shortwave lamps as low-pressure mercury discharge lamps with the 254 nm line, and longwave lamps as phosphor-coated mercury lamps with a strong component near 365 nm. Choosing one is on best UV lamp for mineral collecting; exposure limits are in the ICNIRP 2004 guidelines on limits of exposure to ultraviolet radiation, and this page is not safety advice. More guides are in the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.