Alunogen is a hydrated aluminum sulfate mineral that typically forms as a white, fibrous, or powdery efflorescence in mining environments or volcanic fumaroles. It is extremely soluble and fragile, requiring careful handling and storage in a dry environment to prevent dehydration or dissolution.
Is this alunogen?
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 alunogen with a known reference. Alunogen sits at Mohs 1.5-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Alunogen leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Alunogen typically shows a silky luster.
- 4Match the color rangeCompare against the expected color range: white, yellowish, reddish, colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fibrous, efflorescent crusts, powdery, stalactitic.
Often confused with
Alunogen vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside alunogen
Minerals reported to co-occur with alunogen. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₂(SO₄)₃·17H₂O
- Mohs hardness
- 1.5-2
- Density
- 1.77-1.80 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fibrous, Efflorescent Crusts, Powdery, Stalactitic
- Cleavage
- Perfect in One Direction
- Rarity
- Common
- Uses
- Collector
- Host rock
- Fumaroles and Coal Mine Dumps Where Pyritic Material Undergoes Oxidation
- Typical price
- $10-40 per specimen
Where rockhounds find alunogen
2 mapped spotsClassic worldwide localities
- Chuquicamata, Chile
- Alum Cave, Tennessee, USA
- Vulcano, Italy
- Rio Tinto, Spain
Field-hunting tip
Look in fumaroles and coal mine dumps where pyritic material undergoes oxidation country, the host setting where alunogen typically forms. If you start seeing gypsum, jarosite, melanterite in float, you are in the right ground. Field specimens usually show a fibrous, efflorescent crusts, powdery, stalactitic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri. Start trip planning there.
Common questions
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Find alunogen on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
