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, 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
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Find arcanite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
