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 — that is 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
How do you identify alunogen?+
Where is alunogen found?+
Can I find alunogen in the United States?+
How much is alunogen worth?+
What rocks look like alunogen?+
What minerals are found with alunogen?+
What kind of rock does alunogen form in?+
What is alunogen used for?+
Find alunogen on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
