Clinosulfur is a high-temperature polymorph of elemental sulfur that forms monoclinic crystals, often as a result of rapid cooling near volcanic vents. It is structurally unstable at room temperature and typically reverts to the more common orthorhombic sulfur form over time, making it a challenging and rare acquisition for mineral collectors.

Hardness

1.5-2.5

Mohs

Luster

Resinous

Streak

White

Transparency

Translucent

mineralrareSulfur family

Clinosulphur

Also: Monoclinic Sulfur, Beta-sulfur

Hardness: 1.5-2.5
Luster: Resinous
Streak: White
Transparency: Translucent

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Is this clinosulphur?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch clinosulphur with a known reference. Clinosulphur sits at Mohs 1.5-2.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: resinous.
4
Match the color range
Compare against the expected color range: yellow, pale yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: acicular crystals, encrustations, prismatic.

Often confused with

Clinosulphur vs. its common look-alikes, and how to tell them apart in the field.

mineral

Greenockite

Mohs 3-3.5

How to tell apart: Streak differs, so Clinosulphur leaves white, Greenockite leaves yellow-orange to brick-red; luster reads resinous on Clinosulphur and adamantine to resinous on Greenockite.

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Often found alongside clinosulphur

Minerals reported to co-occur with clinosulphur. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: S₈
Mohs hardness: 1.5-2.5
Density: 2.07 g/cm³
Colors: Yellow Pale yellow
Streak: White
Luster: Resinous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Acicular crystals, encrustations, prismatic
Cleavage: Poor
Rarity: Rare
Uses: Collector, Scientific research
Host rock: volcanic fumaroles, hydrothermal veins

Where rockhounds find clinosulphur

Classic worldwide localities

Italy
Japan
USA
Indonesia

Field-hunting tip

Where it forms: volcanic fumaroles, hydrothermal veins. If you start seeing gypsum, aragonite, celestine in float, you are in the right ground. Typical habit: acicular crystals, encrustations, prismatic. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify clinosulphur?+

Mohs hardness is 1.5-2.5. Luster: resinous. The streak is white. Common colors include yellow, pale yellow.

Where is clinosulphur found?+

Notable localities include Italy; Japan; USA; Indonesia.

What rocks look like clinosulphur?+

Clinosulphur is most often confused with Greenockite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with clinosulphur?+

Clinosulphur commonly co-occurs with Gypsum, Aragonite, Celestine, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does clinosulphur form in?+

Where it forms: volcanic fumaroles, hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is clinosulphur used for?+

Clinosulphur is used in collector, scientific research.

Find clinosulphur on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.