Arcanite is a rare potassium sulfate mineral typically found as a secondary mineral in volcanic fumaroles or as a constituent of salt deposits. It is water-soluble and usually appears as small white to colorless crusts or efflorescences, making it difficult to collect in the field without protection from humidity.
Is this arcanite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch arcanite with a known reference. Arcanite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Arcanite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Arcanite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellowish.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive, crusts, or rare prismatic crystals.
Often confused with
Arcanite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside arcanite
Minerals reported to co-occur with arcanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂SO₄
- Mohs hardness
- 3
- Density
- 2.66 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive, Crusts, Or Rare Prismatic Crystals
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Fumarolic Deposits, Evaporite Deposits
- Typical price
- $20-100 for small specimens
Where rockhounds find arcanite
Classic worldwide localities
- Vesuvius (Italy)
- Potash mines (Germany)
- Potash mines (USA)
Field-hunting tip
Look in fumarolic deposits, evaporite deposits country — that is the host setting where arcanite typically forms. If you start seeing thenardite, aphthitalite, sylvite in float, you are in the right ground. Field specimens usually show a massive, crusts, or rare prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify arcanite?+
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Find arcanite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
