Piccoliite is an extremely rare manganese arsenate mineral known primarily from the Valletta mine in Italy. It typically occurs as small, platy yellow crystals or radial clusters associated with other manganese minerals in metamorphic deposits.

Hardness

Mohs

Luster

Vitreous

Transparency

Translucent

mineralrare

Piccoliite

Hardness: 3
Luster: Vitreous
Transparency: Translucent

Is this piccoliite?

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 piccoliite with a known reference. Piccoliite 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: yellow, brownish-yellow.
4
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy crystals, radial aggregates.

Often confused with

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

mineral

Ferrosilite

Mohs 5-6

How to tell apart: Ferrosilite is the harder of the two (Mohs 5-6 vs. 3).

Compare →

Often found alongside piccoliite

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

All properties

Chemical formula: NaCaMn₂(AsO₄)₂O(OH)
Mohs hardness: 3
Colors: Yellow Brownish-yellow
Luster: Vitreous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Platy crystals, radial aggregates
Rarity: Rare
Uses: Collector
Host rock: manganese-rich metamorphic rocks

Where rockhounds find piccoliite

Classic worldwide localities

Montaldo di Mondovì mine, Borgata Oberti, Montaldo di Mondovì, Corsaglia Valley, and the Valletta mine, Canosio, Maira Valley, Piedmont, Italy

Field-hunting tip

Where it forms: manganese-rich metamorphic rocks. If you start seeing braunite, hausmannite, medite in float, you are in the right ground. Typical habit: platy crystals, radial aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify piccoliite?+

Mohs hardness is 3. Luster: vitreous. Common colors include yellow, brownish-yellow.

Where is piccoliite found?+

Notable localities include Montaldo di Mondovì mine, Borgata Oberti, Montaldo di Mondovì, Corsaglia Valley, and the Valletta mine, Canosio, Maira Valley, Piedmont, Italy.

Is piccoliite safe to handle?+

Piccoliite contains arsenic and calls for real care. Contains arsenic, a toxic element. Wash hands thoroughly after handling and avoid inhaling dust or powder.

What rocks look like piccoliite?+

Piccoliite is most often confused with Ferrosilite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with piccoliite?+

Piccoliite commonly co-occurs with braunite, hausmannite, medite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does piccoliite form in?+

Where it forms: manganese-rich metamorphic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is piccoliite used for?+

Piccoliite is used in collector.

Find piccoliite on the map

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