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 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, yellow, white.
- 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
- 2
- Density
- 2.66 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive, crusts, or rare prismatic crystals
- Cleavage
- On {010} and {001}, good
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In a pine railroad tie (Santa Ana mine, California, USA); in hydrothermally altered rock in a geothermal field (Cesano geothermal field, Italy); derived from bird guano on islands and bat guano in caves
Where rockhounds find arcanite
Classic worldwide localities
- Santa Ana tin mine, Trabuco Canyon, Orange Co., California, USA
- Chincha Islands, off the coast of Peru
- Cesano geothermal field, Latium, Italy
- Arnhem, Arun Aas, Baobab, Gâuan Aas, Né-rab-aas, Temple of Doom, and Uisib Caves, Namibia
- Lobatse Cave, Botswana
- Timbavati Cave, South Africa
Field-hunting tip
Where it forms: In a pine railroad tie (Santa Ana mine, California, USA); in hydrothermally altered rock in a geothermal field (Cesano geothermal field, Italy); derived from bird guano on islands and bat guano in caves. If you start seeing syngenite, swaknoite, mundrabillaite in float, you are in the right ground. Typical habit: massive, crusts, or rare prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify arcanite?+
Where is arcanite found?+
What rocks look like arcanite?+
What minerals are found with arcanite?+
What kind of rock does arcanite form in?+
What is arcanite used for?+
Find arcanite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
