Cadwaladerite is a very rare aluminum hydroxychloride mineral found in arid desert evaporite deposits. It is known for its extreme solubility in water, requiring collectors to keep specimens in sealed containers to prevent deliquescence or dissolution in humid air.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrare

Cadwaladerite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this cadwaladerite?

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 cadwaladerite with a known reference. Cadwaladerite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: lemon.
5
Look at form & habit
Crystal system: amorphous. Typical habit: fine-grained aggregates.

Often confused with

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

Often found alongside cadwaladerite

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

All properties

Chemical formula: AlCl(OH)₂·4H₂O
Mohs hardness: 2
Density: 1.66 g/cm³
Colors: Lemon
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Amorphous
Crystal habit: Fine-grained aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In a sulfate deposit, embedded in halite

Where rockhounds find cadwaladerite

Classic worldwide localities

On mine dumps at Cerro Pintados, 80 km southeast of Iquique, Tarapaca, Chile (type locality)

Field-hunting tip

Where it forms: In a sulfate deposit, embedded in halite. If you start seeing halite, gypsum in float, you are in the right ground. Typical habit: fine-grained aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cadwaladerite?+

Mohs hardness is 2. Luster: vitreous. The streak is white. Common colors include lemon.

Where is cadwaladerite found?+

Notable localities include On mine dumps at Cerro Pintados, 80 km southeast of Iquique, Tarapaca, Chile (type locality).

What rocks look like cadwaladerite?+

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

What minerals are found with cadwaladerite?+

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

What kind of rock does cadwaladerite form in?+

Where it forms: In a sulfate deposit, embedded in halite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cadwaladerite used for?+

Cadwaladerite is used in collector.

Find cadwaladerite on the map

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