Sphalerite
Sphalerite is zinc sulphide, the main zinc ore: hardness 3.5 to 4, density 3.9 to 4.1, resinous to adamantine, iron on 31% of metal sites in one analysis.
Sphalerite is zinc sulphide, ZnS, which the Handbook calls the most important ore of zinc: cubic, hardness 3.5 to 4, density 3.9 to 4.1, resinous to adamantine, with a pale brown to white streak. Iron substitutes for zinc: 31% of the metal atoms in one analysed specimen. Its name means treacherous: it was mistaken for galena.
In short
- The name is a warning about galena. The Handbook of Mineralogy derives sphalerite from the Greek for treacherous, because it was mistaken for galena but yielded no lead. The two are named as associates of each other.
- Galena is nearly twice as heavy. Galena's density is 7.58, sphalerite's 3.9 to 4.1. A 2 cm cube weighs 60.6 g in galena and 31.2 to 32.8 g in sphalerite. The streaks differ too: lead-grey against pale brown to white.
- Iron is what changes it. Pure ZnS is 67.10% zinc. The Handbook's analysis from the St Christoph mine in Isère is 44.67% zinc and 18.25% iron: iron on 31% of the metal sites. The sheet says sphalerite turns opaque when iron-rich.
- It is the only sulphide in this site's reference set recorded as fluorescent. It is also one of just two of the 176 sheets, with quartz, that record both pyroelectricity and triboluminescence.
- Two localities on the sheet have pages here: Alston Moor in Cumbria, the sheet's one English entry, and Dal’negorsk in Primorskiy Kray.
| Species | Formula | Hardness | Density | Streak | Lustre | Cleavage | Zn by mass |
|---|---|---|---|---|---|---|---|
| Sphalerite | ZnS; (Zn,Fe)S in the Handbook | 3.5 to 4 | 3.9 to 4.1 | Pale brown to pale yellow and white | Resinous to adamantine | Perfect on {011}, six directions | 67.10% pure; 44.67% in the iron-rich St Christoph analysis |
| Galena | PbS | 2.5 to 2.75 | 7.58 | Lead-grey | Metallic | Perfect cubic, three directions | 0% |
| Siderite | FeCO3 | 3.75 to 4.25 | 3.96 | White | Vitreous, may be pearly or silky | Perfect rhombohedral, three directions | 0% |
| Cassiterite | SnO2 | 6 to 7 | 6.98 to 7.01 | White, pale brown, pale grey | Adamantine to adamantine metallic | Imperfect | 0% |
| Chalcopyrite | CuFeS2 | 3.5 to 4 | 4.1 to 4.3 | Greenish black | Metallic | Poor | 0% |
| Smithsonite | ZnCO3 | 4 to 4.5 | 4.43 | White | Vitreous, may be pearly | Nearly perfect rhombohedral | 52.14% |
Why is sphalerite called treacherous? The galena test
The Handbook says the name is from the Greek for treacherous, the mineral sometimes being mistaken for galena, but yielding no lead. The confusion is still easy to make. Both are cubic, both occur in the same veins, and both can be dark and bright. Each sheet names the other as an associate.
Three checks separate them. Streak: galena's is lead-grey; sphalerite's is pale brown to pale yellow and white, even when the crystal is black. Weight: galena is 7.58 against 3.9 to 4.1, so it is 1.85 to 1.94 times as heavy for the same size, and a 2 cm cube weighs 60.6 g against 31.2 to 32.8 g. Lustre: galena is metallic; sphalerite is resinous to adamantine. The Handbook's reflectance for sphalerite is 19.6% at 400 nm, falling to 15.8% at 700 nm. The galena sheet gives 51.9% at 400 nm.
The quotable version: a dark cubic sulphide with a pale streak and a resinous lustre is sphalerite, whatever its colour. The methods are on how to use a streak plate and how to measure specific gravity at home. The heavy grey mineral itself is on galena.
What makes sphalerite dark? Iron, calculated
The IMA writes sphalerite as ZnS; the Handbook writes (Zn,Fe)S, because iron substitutes for zinc. The September 2026 IMA-CNMNC Master List gives the formula ZnS and the status line 1980 s.p., a special-procedure action, with the country unknown.
A worked calculation. On standard atomic weights, zinc 65.38 and sulphur 32.06, pure ZnS has a formula mass of 97.44 and is 67.10% zinc, which is the Handbook's ideal column exactly. The sheet then prints two real analyses. The first, from Sonora, Mexico, is 66.98% zinc and 0.15% iron: iron on 0.26% of the metal sites, essentially pure. The second, from the St Christoph mine in Isère, France, is 44.67% zinc, 18.25% iron, 2.66% manganese and 0.28% cadmium. Divided by their atomic weights and set against the sulphur, that is Zn 0.653, Fe 0.312, Mn 0.046 per sulphur. Iron is on 30.8% of the metal sites, which reproduces the sheet's own (Zn0.65Fe0.31Mn0.05).
Why it matters to a collector. The optical line on the sheet reads transparent to translucent, opaque when iron-rich, and the colour runs from colourless to dark brown and black. So a pale, transparent sphalerite and a black, opaque one can be the same species at different iron contents. The streak stays pale in both cases, which is why the streak test works.
Is sphalerite fluorescent? The only sulphide in the set that is
The sheet's physical-properties line reads pyroelectric, may be triboluminescent, fluorescent. Each of the three was counted across the 176 sheets in this site's reference set, converted with pdftotext -layout.
Fluorescence. The search is ligature-aware: it matches fl or the stray glyph that replaces the fl ligature on older sheets. Hemimorphite and willemite are the positive controls, and both match. The search finds 31 sheets recording fluorescence against 21 for a literal search. Of the 27 sheets whose header formula contains sulphur and no oxygen, which is how this page defines the sulphides and sulphosalts in the set, sphalerite is the only one of the 31. It names no colour or UV band, which makes it one of the 12 such sheets listed on is smithsonite UV-reactive. The general picture is on fluorescent minerals explained.
Pyroelectricity and triboluminescence. Pyroelectr appears on 11 sheets and tribolumin on 6. Only quartz and sphalerite appear in both lists, and sphalerite is the only sulphide in either. Triboluminescence is light given off when a mineral is struck or scratched. The other five are calcite, dolomite, fluorite, magnesite and quartz; of those, only dolomite and magnesite are recorded without a may or rarely.
Sphalerite crystals, cleavage and twins
The Handbook describes tetrahedral and dodecahedral crystals, typically complex and distorted, with curved and conical faces common, to 30 cm. It also records fibrous, botryoidal, stalactitic, cleavable and granular forms. Twins are on {111}, as simple contact twins or complex lamellar forms; see mineral twinning explained.
The cleavage is perfect on {011}. In a cubic mineral that is the dodecahedron, which gives six cleavage directions, against galena's three. A broken sphalerite therefore shows many small bright facets at different angles, not the stepped cubes of galena. See cleavage or fracture: how to tell.
The Handbook records sphalerite as trimorphous with matraite and wurtzite. Wurtzite is on the September 2026 IMA list as ZnS, 1861, Bolivia. Matraite does not appear on that list at all (searched by name), so it is not a valid species today. Neither is in this site's reference set.
Where sphalerite is found, including Alston Moor
The sheet's occurrence is broad: low- to high-temperature hydrothermal conditions, and in coal, limestone and other sedimentary deposits, with galena, chalcopyrite, marcasite, pyrite, fluorite, baryte, quartz and many other hydrothermal minerals. Sphalerite is named in the Association field of 16 of the other 175 sheets in the set. These run from galena, chalcopyrite and tetrahedrite to hemimorphite, rhodochrosite and cronstedtite.
The Handbook says only a few localities for the finest crystallised examples can be given. In Germany it names Freiberg in Saxony and Neudorf in the Harz. It also names colourless crystals from the Lengenbach quarry, Binntal; Horní Slavkov and Příbram in the Czech Republic; Rodna in Romania; and transparent crystals from the Aliva mine, Picos de Europa, Spain. In England it names Alston Moor, Cumbria. Further afield are Dal’negorsk, Russia, and Watson Lake, Yukon. In the USA it lists the Tri-State district, with Baxter Springs, Joplin and Picher; the Elmwood mine near Carthage, Tennessee; and the Eagle mine at Gilman, Colorado. It ends with Santa Eulalia, Naica and Cananea in Mexico, and Huaron, Casapalca and Huancavelica in Peru.
Sphalerite's oxidation products, smithsonite and hemimorphite, have their own pages. The rest of the sulphides are indexed at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.