Petersenite-(Ce) is an extremely rare rare-earth carbonate almost exclusively found in the alkaline complex of Mont Saint-Hilaire. It typically forms thin, delicate platy crystals in cavities within pegmatites or syenites. Due to its extreme rarity and small crystal size, it is a highly sought-after species for specialized mineral collectors.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrare

Petersenite-(Ce)

Hardness: ~3
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this petersenite-(ce)?

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 petersenite-(ce) with a known reference. Petersenite-(Ce) sits at Mohs ~3, 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: light violet, light yellow, pink gray, reddish gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: acicular, prismatic.

Often confused with

Petersenite-(Ce) vs. its common look-alikes, and how to tell them apart in the field.

mineral

Eudialyte

Mohs 5-6

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

Compare →

Often found alongside petersenite-(ce)

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

All properties

Chemical formula: Na₄Ce₂(CO₃)₅
Mohs hardness: ~3
Density: 3.69 g/cm³
Colors: Light violet Light yellowPink grayReddish gray
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Monoclinic
Crystal habit: Acicular, prismatic
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A rare component in pegmatites in nepheline–sodalite syenite near a contact with a hornfels unit, associated with an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada)

Where rockhounds find petersenite-(ce)

Classic worldwide localities

Mont Saint-Hilaire, Quebec, Canada
Mt. Koashva, Khibiny massif, Kola Peninsula, Russia

Field-hunting tip

Where it forms: A rare component in pegmatites in nepheline–sodalite syenite near a contact with a hornfels unit, associated with an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada). If you start seeing aegirine, albite, microcline in float, you are in the right ground. Typical habit: acicular, prismatic. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify petersenite-(ce)?+

Mohs hardness is ~3. Luster: vitreous. The streak is white. Common colors include light violet, light yellow, pink gray, reddish gray.

Where is petersenite-(ce) found?+

Notable localities include Mont Saint-Hilaire, Quebec, Canada; Mt. Koashva, Khibiny massif, Kola Peninsula, Russia.

What rocks look like petersenite-(ce)?+

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

What minerals are found with petersenite-(ce)?+

Petersenite-(Ce) commonly co-occurs with Aegirine, Albite, Microcline, Biotite, Chlorite, Polylithionite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does petersenite-(ce) form in?+

Where it forms: A rare component in pegmatites in nepheline–sodalite syenite near a contact with a hornfels unit, associated with an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada). Working float back to the host body is the standard way to chase a fresh occurrence.

What is petersenite-(ce) used for?+

Petersenite-(Ce) is used in collector.

Find petersenite-(ce) on the map

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