Lanmuchangite is a very rare aluminum sulfate mineral typically found as white, needle-like or fibrous coatings on mine walls. It is primarily known from its type locality in the Lanmuchang deposit of China, where it forms in association with cinnabar and other hydrothermal minerals. Collectors should handle specimens with care due to their delicate, friable, and water-soluble nature.

Hardness

3.1-3.4

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrarePickeringite Group family

Lanmuchangite

Hardness: 3.1-3.4
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this lanmuchangite?

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 lanmuchangite with a known reference. Lanmuchangite sits at Mohs 3.1-3.4, 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, light yellow.
5
Look at form & habit
Crystal system: cubic. Typical habit: aggregates, anhedral grains, water soluble.

Often confused with

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

mineral

Pickeringite

Mohs 1.5

How to tell apart: Lanmuchangite is noticeably harder (Mohs 3.1-3.4 vs. 1.5).

How to tell apart: Lanmuchangite is noticeably harder (Mohs 3.1-3.4 vs. 1.5).

Compare →

Often found alongside lanmuchangite

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

All properties

Chemical formula: TlAl(SO₄)₂(H₂O)₁₂
Mohs hardness: 3.1-3.4
Density: 2.22 g/cm³
Colors: White Light yellow
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Cubic
Crystal habit: Aggregates, anhedral grains, water soluble
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: In the oxidation zone of a Tl–Hg deposit

Where rockhounds find lanmuchangite

Classic worldwide localities

Lanmuchang Tl–Hg deposit, Xinren Co., Guizhou Province, China (type locality)

Field-hunting tip

Where it forms: In the oxidation zone of a Tl–Hg deposit. If you start seeing melanterite, pickeringite, jarosite in float, you are in the right ground. Typical habit: aggregates, anhedral grains, water soluble. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify lanmuchangite?+

Mohs hardness is 3.1-3.4. Luster: vitreous. The streak is white. Common colors include white, light yellow.

Where is lanmuchangite found?+

Notable localities include Lanmuchang Tl–Hg deposit, Xinren Co., Guizhou Province, China (type locality).

Is lanmuchangite safe to handle?+

Lanmuchangite contains thallium and calls for real care. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.

What rocks look like lanmuchangite?+

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

What minerals are found with lanmuchangite?+

Lanmuchangite commonly co-occurs with Melanterite, Pickeringite, Jarosite, Gypsum, Potassium alum, Arsenolite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does lanmuchangite form in?+

Where it forms: In the oxidation zone of a Tl–Hg deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is lanmuchangite used for?+

Lanmuchangite is used in collector.

Find lanmuchangite on the map

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