Aluminite is a soft, earthy hydrous aluminum sulfate that typically forms as white, chalky-looking masses or crusts. It is most commonly found in clay formations associated with the weathering of pyrite or other sulfur-bearing minerals.

Hardness

1-2

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

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Aluminite

Hardness: 1-2
Luster: Dull
Streak: White
Transparency: Opaque

Is this aluminite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch aluminite with a known reference. Aluminite sits at Mohs 1-2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Aluminite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Aluminite typically shows a dull luster.
4
Match the color range
Compare against the expected color range: white, grayish-white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: massive, reniform, or earthy crusts.

Often confused with

Aluminite vs. its common look-alikes — and how to tell them apart in the field.

How to tell apart: Luster reads dull on Aluminite and vitreous on Gibbsite.

How to tell apart: Luster reads dull on Aluminite and pearly on Halloysite.

Compare →

Often found alongside aluminite

Minerals reported to co-occur with aluminite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Al₂SO₄(OH)₄·7H₂O
Mohs hardness: 1-2
Density: 1.7 g/cm³
Colors: White Grayish-white
Streak: White
Luster: Dull
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Massive, Reniform, Or Earthy Crusts
Cleavage: None
Rarity: Uncommon
Uses: Collector
Host rock: Clay-rich Sedimentary Deposits
Typical price: $10-50 per specimen

Where rockhounds find aluminite

Classic worldwide localities

Newhaven, England
Halle, Germany
Apt, France
La Spezia, Italy

Field-hunting tip

Look in clay-rich sedimentary deposits country — that is the host setting where aluminite typically forms. If you start seeing gypsum, allophane, limonite in float, you are in the right ground. Field specimens usually show a massive, reniform, or earthy crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify aluminite?+

Mohs hardness is 1-2. It typically shows a dull luster. The streak is white. Common colors include white, grayish-white.

Where is aluminite found?+

Notable localities include Newhaven, England; Halle, Germany; Apt, France; La Spezia, Italy.

How much is aluminite worth?+

Typical asking prices fall in the range of $10-50 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like aluminite?+

Aluminite is most often confused with Kaolinite, Gibbsite, Halloysite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with aluminite?+

Aluminite commonly co-occurs with Gypsum, Allophane, Limonite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does aluminite form in?+

Aluminite typically forms in clay-rich sedimentary deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is aluminite used for?+

Aluminite is used in collector.

Find aluminite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.