Sulfur
S · Orthorhombic · also called brimstone, native sulphur
Native sulfur is the bright yellow crust around volcanic vents and hot springs, and it also occurs in salt-dome cap rock. Its colour is essentially unmistakable, and its habit of cracking apart in a warm hand is a memorable quirk.
Properties
- Mohs hardness
- 1.5–2.5
- Streak
- white, pale yellow
- Lustre
- resinous, greasy, adamantine
- Colour
- A bright, almost fluorescent-looking canary yellow that nothing else common matches.
- Cleavage
- Poor cleavage; usually breaks unevenly.
- Fracture
- Conchoidal to uneven, very brittle
- Specific gravity
- 2.05–2.09 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm sulfur
- Smells faintly of sulfur when rubbed or warmed.
- Crackles and may crumble from the warmth of your hand — it is a poor conductor and heats unevenly.
- Extremely light and very soft.
What sulfur gets confused with
Each of these is settled by one test. Run that test first.
Orpiment
Orpiment is more orange-yellow, peels into flakes, and contains arsenic — handle with care.
Sulfur-stained rock
Genuine sulfur is a solid mass, not a surface stain, and is soft throughout.
Where it is found
Volcanic fumaroles, hot springs, and sedimentary sulfur deposits associated with salt domes.
Is it worth anything?
Inexpensive. Well-formed crystals from Sicily are the classic collectible form.