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Native Element · Native non-metal — sulphur group · Sulphur Group

Sulphur

S

Brimstone made real — lemon-yellow crystals that melt in a hot oven’s heat and burn with an eerie blue flame.

Hardness1.5–2.5
Crystal systemOrthorhombic
LusterResinous
Sp. gravity2.05–2.09
ClassNative Element
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Sulphur specimen

Bipyramidal sulphur crystals — the classic brimstone habit — Photo: Ivar Leidus · CC BY-SA 4.0

What is Sulphur?

Sulphur is a chemical element found in nature as a mineral — pure S, and one of the very few non-metals to occur natively. Its lemon-yellow crystals are unmistakable, and so is its résumé: this is brimstone, the ‘burning stone’ of the ancient world.

Sulfur’s atoms link into crown-shaped rings of eight. That ring is weak, and it shows in every property: sulfur is soft, light, brittle, and melts at about 113 °C — cooler than boiling water is at altitude. Heated a little past its melting point it catches fire and burns with a thin blue flame, releasing the sharp, choking gas sulfur dioxide — the smell behind ‘fire and brimstone’ and, unfairly, rotten eggs (that’s actually hydrogen sulfide).

You’ll find it wherever sulfur-rich gases or waters reach the surface: crusting volcanic vents, lining hot springs, and filling the caprock of salt domes. Warm a specimen in your hand and it faintly crackles — sulfur expands with heat faster than it can conduct the warmth away.

In one sentence: Sulfur is bright yellow, very soft (1.5–2.5), light for its size, resinous rather than glassy, and it melts easily — a specimen held in a warm hand even crackles faintly.

Physical Properties

The full data table is in the panel alongside. Here’s what those numbers actually mean.

Color and luster. The yellow is the thing — a slightly waxy, resinous shine on anything from canary-yellow crystals to dull crusts. Impurities push it toward orange or brownish.

Softness and fragility. At hardness 1.5–2.5 it is scratched by a fingernail, and it’s brittle — sulfur specimens are among the most fragile in any collection.

Heat sensitivity. Sulfur is a thermal insulator that expands a lot when warmed, so a cool crystal brought to a warm hand crackles as its surface strains. Melt it and it turns amber, then thickens into a dark, rubbery liquid; light it and it burns blue.

Solubility. Sulfur shrugs off water and most acids — which is part of why it survives at oxidizing mine dumps and fumaroles where its sulfide cousins rot away.

How & Where It Forms

Sulfur crystallizes where the element is freed from other compounds. At volcanoes, sulfur-bearing gases (SO₂ and H₂S) react at fumarole vents and deposit the element directly — the origin of the encrusting yellow ‘flowers of sulfur’.

Underground, bacteria do similar chemistry: in the caprock of salt domes and in evaporite beds, microbes convert gypsum and anhydrite into calcite plus native sulfur — ore mined by melting it out with superheated water (the Frasch process). Sulfur also weathers out of sulfide ore bodies, which is why it crusts the walls of old mines.

Often grows alongside:

GypsumCalciteCelestineRealgarOrpimentCinnabar

What It’s Used For

Sulfuric acidAround 85% of mined sulfur becomes H₂SO₄ — the most-produced industrial chemical, used to make fertilizer, batteries and much more.
RubberVulcanization — sulfur cross-links rubber so it stays firm instead of sticky.
Matches & fireworksSulfur ignites easily, which made it the fuel of early matches, gunpowder and pyrotechnics.
Farms & pharmaciesOne of the oldest fungicides and pesticides, and an ingredient in skin medicines and soaps.

How to Identify It

Sulfur is bright yellow, soft, light and resinous — scratchable with a fingernail and far lighter than any yellow metal ore. It crackles in a warm hand and, on a pinhead tested outdoors, melts then burns blue with a sulfurous smell. Orpiment is flakier and smells of garlic; carnotite is powdery, never crystalline.

Bright yellow color with a resinous, slightly greasy shineVery soft (1.5–2.5) — a fingernail marks itLight (SG ~2.1) and brittleCrackles faintly when held in a warm hand — it expands faster than it conducts the heat awayMelts near 113 °C and burns with a blue flame plus a choking sulfur smell — try this only on a pinhead, outdoors
Looks like…But differs because…Quick test
OrpimentAlso yellow, but flaky and micaceous rather than resinous, and smells of garlic when crushed; streak is a paler yellowStreak & smell
CarnotiteBright yellow but always a powdery, earthy crust — never crystalline, never resinousLuster & habit
LimoniteYellow-brown earthy coatings with a yellow-brown streak; no resinous shine and won’t meltStreak

Where It’s Found

Notable localities for fine specimens:

Racalmuto & Cianciana, Italy Kawah Ijen, Indonesia El Desierto Mine, Bolivia Steamboat Springs, USA Machów Mine, Tarnobrzeg, PolandOpen the locality map →

References & Further Reading

  1. Dana’s New Mineralogy, 8th ed. Native elements — sulfur group.
  2. Mindat.org — Sulphur mineral data and locality records.
  3. Wikipedia — Sulfur.

Last reviewed 2026-09-14 · How to cite this page.