Is sulfur a mineral?
Yes: native sulfur, S, has an IMA row spelt Sulphur, hardness 1.5 to 2.5. Sulfur from a mine fire fails the 1995 IMA definition, and so does refinery sulfur.
Yes. Native sulfur is a mineral: the September 2026 IMA list gives it a row, spelt Sulphur, formula S, status G, and the Handbook sheet records orthorhombic crystals to 20 cm, hardness 1.5 to 2.5, density 2.07. The qualification is origin: the IMA’s 1995 definition does not accept compounds caused by mine fires, and refinery sulfur is manufactured.
In short
- The row is spelt Sulphur. A script over the September 2026 IMA-CNMNC Master List finds Sulphur, S, status G, year printed as ?, country unknown, and no row spelt Sulfur. The Handbook of Mineralogy sheet is headed Sulfur and filed as sulphur.pdf: one species, two spellings.
- Three rows with the formula S. The same script finds sulphur, rosickýite (G, 1931, Czech Republic) and clinosulphur (Rn, renamed, 2022 s.p., Italy). The sulfur sheet calls it dimorphous with rosickýite; the rosickýite sheet says rosickýite changes to sulfur in time at room temperature.
- The mine-fire clause. Nickel (1995), the IMA commission’s definition of a mineral says compounds caused by mine fires are not accepted as minerals, because it is not always clear whether people started the fire. The sulfur sheet lists four ways sulfur forms, and one is the decomposition of sulfides, especially pyrite, during mine fires. Fumarole sulfur passes, salt-dome sulfur passes on the biogenic clause as this page reads it, and mine-fire sulfur is the route the definition sets aside.
- Most sulfur produced is not a specimen. The USGS Mineral Commodity Summaries 2025 says US elemental sulfur was recovered at petroleum refineries, natural-gas-processing plants and coking plants, and that most sulfur production results from processing fossil fuels. On the 1995 definition, substances produced by people are not minerals.
- Where yes stops meaning natural. The International Gem Society records synthetic crystals grown on authentic Sicilian matrix around 1975, arranged to look like prized Sicilian specimens and difficult to distinguish from them.
| Sulfur, by origin | Source | Example the source names | 1995 clause | A mineral? |
|---|---|---|---|---|
| Sublimate at volcanic fumaroles | Handbook sheet | The sheet does not tie its localities to a route | Formed by geological processes | Yes |
| Low-oxidation, acidic reactions in mineral deposits; in sedimentary rocks | Handbook sheet | The sheet does not tie its localities to a route | Formed by geological processes | Yes |
| Activity of micro-organisms; bacteria on sulfate minerals in salt domes | Handbook sheet; IGS | Large deposits in salt domes, Louisiana and Texas (sheet); bacteria in salt domes (IGS) | Biogenic, with a geological component: can be accepted | Yes, on the clause |
| Decomposition of sulfides, especially pyrite, during mine fires | Handbook sheet | None named | Compounds caused by mine fires are not accepted | No, under the 1995 text |
| Recovered at refineries, gas plants and coking plants | USGS 2025 | 86 US operations in 26 states, 2024 (with byproduct acid) | Anthropogenic: not a mineral | No: manufactured |
| Crystals grown on Sicilian matrix, about 1975 | IGS, citing Pagano | Sold as natural Sicilian sulfur | Anthropogenic: synthetic equivalent | No |
| Rosickýite, S | IMA list; Handbook sheet | Havírna, Czech Republic (type locality); Death Valley | Own species, G, 1931 | Yes, a separate species |
| Clinosulphur, S | IMA list | Country Italy; no Handbook sheet | Own species, Rn, 2022 s.p. | Yes, a separate species |
Is sulfur a mineral? The IMA row and the sheet
Yes: native sulfur is a mineral species. A script over the September 2026 IMA-CNMNC Master List (a row is a line whose first word is the name) finds Sulphur, formula S, status G for grandfathered, with the year printed as ? and the country unknown: known before the IMA existed and generally considered valid. It finds no row spelt Sulfur. The list uses one spelling; the Handbook sheet’s heading uses the other.
On the sheet. The Handbook sulfur sheet, read from the rendered page: orthorhombic, point group 2/m 2/m 2/m; crystals dipyramidal, thick tabular and disphenoidal, to 20 cm; also massive, reniform, stalactitic and as a powder. Cleavage imperfect; fracture conchoidal to uneven; tenacity rather brittle to somewhat sectile. Hardness 1.5 to 2.5; density 2.07 measured. Sulfur-yellow to honey-yellow, yellowish brown, greenish, reddish or yellowish grey, and may be black from included organic matter. Streak white; lustre resinous to greasy. Biaxial (+), α = 1.9579, β = 2.0377, γ = 2.2452. Chemistry: sulfur, sometimes with Se and Te.
An element, like gold and diamond. The formula is the element alone: native sulfur, like gold and diamond, is an element that occurs as a mineral. The general definition and the element question are worked on is gold a mineral and is diamond a mineral; the clause-by-clause test is on is quartz a mineral. None of their assets is repeated here.
How many minerals are sulfur? Three rows with the formula S
Three. The script lists every row whose formula field is exactly S: sulphur (G); rosickýite (G, 1931, Czech Republic, second reference Acta Crystallographica C49 (1993), 125); and clinosulphur (Rn, 2022 s.p., Italy). The list’s own key defines Rn as renamed, an existing mineral renamed during the IMA era, and s.p. as the year of the special procedure.
What the sheets add. The sulfur sheet says only that it is dimorphous with rosickýite; it names no third form. The rosickýite sheet describes monoclinic crystals to 1 mm, colourless to pale yellow with a greenish tinge, with type material in the Moravian Museum, Brno, and says it changes to sulfur in time at room temperature. The Handbook has no clinosulphur sheet (the URL returns 404), so this page states its IMA row and nothing more.
Weight, for completeness. At the sheet’s 2.07, a 20.00 g piece of sulfur reads 10.34 g in water; the gem society’s SG 2.05 to 2.09 gives 10.24 to 10.43 g. Quartz reads 12.45 g. The method is on how to measure specific gravity at home.
When is sulfur not a mineral? The mine-fire clause
The mine-fire clause: under the IMA commission’s 1995 definition, chemical compounds caused by mine fires are not accepted as minerals, and mine fires are one of the four ways of forming that the sulfur sheet gives. Nickel (1995), the IMA commission’s definition of a mineral treats them as a special case, because it is not always clear whether there has been human involvement in starting the fire. The sheet’s Occurrence field reads: a sublimation product at volcanic fumaroles; a product of the activity of biological micro-organisms; a result of low oxidation potential and highly acidic reactions in mineral deposits; formed by the decomposition of sulfides, especially pyrite, during mine fires; and found in sedimentary rocks.
What the clause does and does not do. The definition says it is not retroactive, so it does not unmake sulphur as a species; the species stands on its G row. It tells a collector which material the definition itself would not count as the basis of a mineral: sulfur formed in a mine fire. The sheet names no mine-fire locality, and this page adds none.
The biogenic clause, on salt-dome sulfur. The 1995 text says substances produced entirely by biological processes without a geological component are not minerals, but if geological processes were involved the product can be accepted. The sheet records large deposits in salt domes in Louisiana and Texas, and the International Gem Society says anaerobic bacteria acting on sulfate minerals can produce native sulfur in salt domes. On this page’s reading, bacteria acting on sulfate minerals inside a salt dome is a geological setting, which the clause allows; the 1995 text does not discuss sulfur by name.
Refinery sulfur and grown crystals: not minerals
Recovered sulfur is manufactured. The USGS Mineral Commodity Summaries 2025, Sulfur says that in 2024 recovered elemental sulfur and byproduct sulfuric acid were produced at 86 operations in 26 states, that elemental sulfur was recovered, in descending order of tonnage, at petroleum refineries, natural-gas-processing plants and coking plants, and that most sulfur production is a result of the processing of fossil fuels. On the 1995 definition, substances produced by people are not minerals; one identical to a mineral may be called a synthetic equivalent.
Documented failure: grown crystals on real matrix. The International Gem Society sulfur article (Arem, updated July 2023) says that around 1975 an Italian natural history enthusiast created and sold synthetic crystals designed to look like top-quality Sicilian sulfur, grown on authentic Sicilian matrix, that he admitted it in 2000, and that they proved difficult to distinguish from natural Sicilian specimens. The crystals are sulfur, but grown, not formed: synthetic equivalents. A real matrix does not prove a natural crystal.
What the sheet says about Sicily. It names Cianciana and Racalmuto, Agrigento, as the source of exceptionally large and fine crystals. The gypsum sheet names the same two places, and the sulfur sheet lists gypsum first among its associates.
Sulfur in gypsum and anhydrite
Native sulfur and the sulphates. The sulfur sheet lists gypsum, anhydrite, halite, aragonite, calcite and celestine as associates. The USGS calls the sulfur in gypsum and anhydrite almost limitless. Worked on standard atomic weights, sulfur is 23.55% of anhydrite and 18.62% of gypsum by mass, but in those minerals it is sulphate, not the element. Telling the two sulphates apart is on is anhydrite gypsum.
Hazard. Sulfur dust, burning sulfur and sulfur compounds raise questions this page does not answer; see toxic minerals in a collection, and it is not advice. The definitions guides are in the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.