Yanomamite is an extremely rare indium arsenate mineral found in specific hydrothermal environments. Collectors generally look for its distinctive yellow to yellow-green micro-crystalline crusts which appear in association with arsenopyrite deposits.

Hardness

3.5-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrare

Yanomamite

Hardness: 3.5-4
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this yanomamite?

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 yanomamite with a known reference. Yanomamite sits at Mohs 3.5-4, 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: blue green, light green, light yellow green.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: microcrystalline crusts, tiny tabular crystals.

Often confused with

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

mineral

Scorodite

Mohs 3.5-4

How to tell apart: Streak differs, so Yanomamite leaves white, Scorodite leaves greenish white.

Often found alongside yanomamite

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

All properties

Chemical formula: InAsO₄·2H₂O
Mohs hardness: 3.5-4
Density: 3.87 g/cm³
Colors: Blue green Light greenLight yellow green
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Microcrystalline crusts, tiny tabular crystals
Cleavage: Indistinct
Rarity: Rare
Uses: Collector
Host rock: A rare secondary mineral replacing arsenopyrite in quartz-topaz greisen veins in granite

Where rockhounds find yanomamite

Classic worldwide localities

Mangabeira tin deposit, near Passa e Fica, Goiás, Brazil

Field-hunting tip

Where it forms: A rare secondary mineral replacing arsenopyrite in quartz-topaz greisen veins in granite. If you start seeing scorodite, arsenopyrite, indium-rich sphalerite in float, you are in the right ground. Typical habit: microcrystalline crusts, tiny tabular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify yanomamite?+

Mohs hardness is 3.5-4. Luster: vitreous. The streak is white. Common colors include blue green, light green, light yellow green.

Where is yanomamite found?+

Notable localities include Mangabeira tin deposit, near Passa e Fica, Goiás, Brazil.

Is yanomamite safe to handle?+

Yanomamite contains arsenic and calls for real care. Contains arsenic. Wash hands thoroughly after handling and avoid inhaling dust or ingesting particles.

What rocks look like yanomamite?+

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

What minerals are found with yanomamite?+

Yanomamite commonly co-occurs with Scorodite, Arsenopyrite, Indium-rich sphalerite, Topaz, Cassiterite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does yanomamite form in?+

Where it forms: A rare secondary mineral replacing arsenopyrite in quartz-topaz greisen veins in granite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is yanomamite used for?+

Yanomamite is used in collector.

Find yanomamite on the map

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