Hydrobasaluminite is a rare, unstable aluminum sulfate mineral typically found as white, chalky crusts or powdery aggregates in clay-rich environments. Collectors often find it in association with gypsum in deposits undergoing weathering. It is notable for its high water content and tendency to dehydrate, eventually altering into basaluminite.
Is this hydrobasaluminite?
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 hydrobasaluminite with a known reference. Hydrobasaluminite 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: earthy.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: earthy.
Often confused with
Hydrobasaluminite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hydrobasaluminite
Minerals reported to co-occur with hydrobasaluminite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₄SO₄(OH)₁₀·12-36H₂O
- Mohs hardness
- 2
- Density
- 1.86 g/cm³
- Colors
- Streak
- White
- Luster
- Earthy
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Earthy
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Infilling vertical fissures in the weathering zone of siderite–chamosite ironstones (Irchester, England)
Where rockhounds find hydrobasaluminite
Classic worldwide localities
- Three km west of Shoals, Martin Co., Indiana, USA
- Cottonwood Cave, Guadalupe Mountains, New Mexico, USA
- Holbrook pit and in the Southwest mine, Bisbee, Cochise Co., Arizona, USA
- Lodge pit, Irchester, Northamptonshire, England
- Clifton Hill, Brighton, Sussex, England
- Crook Hill Brickyard, Chickerell, near Weymouth, Dorset, England
Field-hunting tip
Where it forms: Infilling vertical fissures in the weathering zone of siderite–chamosite ironstones (Irchester, England). If you start seeing basaluminite, gypsum, aragonite in float, you are in the right ground. Typical habit: earthy. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hydrobasaluminite?+
Where is hydrobasaluminite found?+
What rocks look like hydrobasaluminite?+
What minerals are found with hydrobasaluminite?+
What kind of rock does hydrobasaluminite form in?+
What is hydrobasaluminite used for?+
Find hydrobasaluminite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
