Walthierite is a rare barium-dominant member of the alunite group often found in hydrothermally altered volcanic environments. Collectors typically look for small, white, platy crystals or granular masses formed within acid-sulfate leaching zones.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrareAlunite Supergroup family

Walthierite

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Transparent

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Is this walthierite?

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 walthierite with a known reference. Walthierite sits at Mohs 3-4, 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: white, yellowish.
5
Look at form & habit
Crystal system: trigonal. Typical habit: platy crystals, granular aggregates.

Often confused with

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

How to tell apart: Streak differs, so Walthierite leaves white, Jarosite leaves pale yellow; luster reads vitreous on Walthierite and subadamantine to vitreous, resinous on fractures on Jarosite.

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Often found alongside walthierite

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

All properties

Chemical formula: Ba₀.₅Al₃(SO₄)₂(OH)₆
Mohs hardness: 3-4
Density: 3.02 g/cm³
Colors: White Yellowish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Platy crystals, granular aggregates
Cleavage: On {001}, perfect
Rarity: Rare
Uses: Collector
Host rock: Rare, in open-space filling of a fault, formed by reaction of hydrothermal fluids with barite

Where rockhounds find walthierite

Classic worldwide localities

Reina vein, about seven km southeast of the El Indio mine, El Indio-Tambo district, east of La Serena, Coquimbo, Chile

Field-hunting tip

Where it forms: Rare, in open-space filling of a fault, formed by reaction of hydrothermal fluids with barite. If you start seeing alunite, barite, jarosite in float, you are in the right ground. Typical habit: platy crystals, granular aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify walthierite?+

Mohs hardness is 3-4. Luster: vitreous. The streak is white. Common colors include white, yellowish.

Where is walthierite found?+

Notable localities include Reina vein, about seven km southeast of the El Indio mine, El Indio-Tambo district, east of La Serena, Coquimbo, Chile.

What rocks look like walthierite?+

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

What minerals are found with walthierite?+

Walthierite commonly co-occurs with Alunite, Barite, Jarosite, Pyrite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does walthierite form in?+

Where it forms: Rare, in open-space filling of a fault, formed by reaction of hydrothermal fluids with barite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is walthierite used for?+

Walthierite is used in collector.

Find walthierite on the map

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