Ambrinoite is a rare potassium arsenic antimony oxide, typically cinnabar-red. It occurs in an evaporite deposit probably formed by highly alkaline, low-temperature hydrothermal fluids. Associated minerals include sulfur, orpiment and gypsum. It was first described from the Cumbë Sûrdë quarry, Signols, Oulx, Upper Susa Valley, Torino, Piedmont, Italy.

Hardness

5-6

Mohs

Luster

Vitreous to Resinous

Streak

Reddish

Transparency

Transparent

mineralrareAeschynite Group family

Ambrinoite

Hardness: 5-6
Luster: Vitreous to Resinous
Streak: Reddish
Transparency: Transparent

Is this ambrinoite?

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 ambrinoite with a known reference. Ambrinoite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ambrinoite leaves a reddish streak.
3
Read the luster
Hold the specimen under a strong light. Ambrinoite typically shows a vitreous to resinous luster.
4
Match the color range
Compare against the expected color range: cinnabar-red.
5
Look at form & habit
Crystal system: triclinic. Typical habit: prismatic crystals.

Often confused with

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

mineral

Euxenite-(Y)

Mohs 5.5-6.5

How to tell apart: Streak differs, so Ambrinoite leaves reddish, Euxenite-(Y) leaves yellowish-brown; luster reads vitreous to resinous on Ambrinoite and submetallic on Euxenite-(Y).

Compare →

Often found alongside ambrinoite

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

All properties

Chemical formula: [K,(NH₄)]₂(As,Sb)₆(Sb,As)₂S₁₃·H₂O
Mohs hardness: 5-6
Density: 3.276 g/cm³
Colors: Cinnabar-red
Streak: Reddish
Luster: Vitreous to Resinous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Prismatic Crystals
Cleavage: Perfect On {001} and {010}, Poor On {100}
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites

Where rockhounds find ambrinoite

Classic worldwide localities

Cumbë Sûrdë quarry, Piedmont, Italy

Field-hunting tip

Look in granite pegmatites country, the host setting where ambrinoite typically forms. If you start seeing zircon, monazite, feldspar in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ambrinoite?+

Mohs hardness is 5-6. It typically shows a vitreous to resinous luster. The streak is reddish. Common colors include cinnabar-red.

Where is ambrinoite found?+

Notable localities include Cumbë Sûrdë quarry, Piedmont, Italy.

Is ambrinoite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains antimony and arsenic, which are toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ambrinoite?+

Ambrinoite is most often confused with Euxenite-(Y). A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with ambrinoite?+

Ambrinoite commonly co-occurs with Zircon, Monazite, Feldspar, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ambrinoite form in?+

Ambrinoite typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ambrinoite used for?+

Ambrinoite is used in collector.

Find ambrinoite on the map

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