Favreauite is an incredibly rare lead-bismuth-copper selenite mineral known almost exclusively from the Poudrette quarry at Mont Saint-Hilaire. It typically forms small, green, translucent tabular crystals or crusts in vugs within alkaline igneous rocks. Collectors prize this species for its intense color and status as a type-locality rarity.

Hardness

Mohs

Luster

Vitreous

Transparency

Transparent

mineralrare

Favreauite

Hardness: ~3
Luster: Vitreous
Transparency: Transparent

Is this favreauite?

4-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 favreauite with a known reference. Favreauite sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
2
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
3
Match the color range
Compare against the expected color range: green.
4
Look at form & habit
Crystal system: tetragonal. Typical habit: tabular crystals, crusts, aggregates.

Often confused with

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

Often found alongside favreauite

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

All properties

Chemical formula: PbBiCu₆O₄(SeO₃)₄(OH)·H₂O
Mohs hardness: ~3
Density: 4.851 g/cm³
Colors: Green
Luster: Vitreous
Transparency: Transparent
Crystal system: Tetragonal
Crystal habit: Tabular crystals, crusts, aggregates
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral formed by the oxidation of a selenide-bearing hydrothermal vein hosted by sandstones and shales

Where rockhounds find favreauite

Classic worldwide localities

El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia

Field-hunting tip

Where it forms: A secondary mineral formed by the oxidation of a selenide-bearing hydrothermal vein hosted by sandstones and shales. If you start seeing ahlfeldite, allophane, calcite in float, you are in the right ground. Typical habit: tabular crystals, crusts, aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify favreauite?+

Mohs hardness is ~3. Luster: vitreous. Common colors include green.

Where is favreauite found?+

Notable localities include El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia.

Is favreauite safe to handle?+

Favreauite contains copper, lead and selenium. Contains lead and selenium; wash hands thoroughly after handling and avoid inhaling dust.

What rocks look like favreauite?+

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

What minerals are found with favreauite?+

Favreauite commonly co-occurs with Ahlfeldite, Allophane, Calcite, Chalcomenite, Malachite, Molybdomenite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does favreauite form in?+

Where it forms: A secondary mineral formed by the oxidation of a selenide-bearing hydrothermal vein hosted by sandstones and shales. Working float back to the host body is the standard way to chase a fresh occurrence.

What is favreauite used for?+

Favreauite is used in collector.

Find favreauite on the map

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