Thorbastnäsite is a rare thorium-dominant member of the bastnäsite group, typically found as tiny, brownish to yellow platy crystals. It is primarily sought after by specialized rare-earth element collectors due to its radioactive nature and association with unique pegmatite and skarn environments.

Hardness

4-4.5

Mohs

Luster

Vitreous to greasy

Streak

White

Transparency

Semitransparent

mineralrareBastnäsite Group family

Thorbastnäsite

Hardness: 4-4.5
Luster: Vitreous to greasy
Streak: White
Transparency: Semitransparent

Is this thorbastnäsite?

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 thorbastnäsite with a known reference. Thorbastnäsite sits at Mohs 4-4.5, 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 to greasy.
4
Match the color range
Compare against the expected color range: brown.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: platy crystals, granular aggregates.

Often confused with

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

Often found alongside thorbastnäsite

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

All properties

Chemical formula: ThCa(CO₃)₂F₂·3H₂O
Mohs hardness: 4-4.5
Density: 4.04 g/cm³
Colors: Brown
Streak: White
Luster: Vitreous to greasy
Transparency: Semitransparent
Crystal system: Hexagonal
Crystal habit: Platy crystals, granular aggregates
Cleavage: Distinct
Rarity: Rare
Uses: Collector
Host rock: In metasomatic albitite and quartz–muscovite veinlets in an alkaline exocontact surrounding a syenite intrusive

Where rockhounds find thorbastnäsite

Classic worldwide localities

Pichikhol alkaline massif, Balygtyg-Khem River, Sangilen Upland, Tuva, Siberia, Russia

Field-hunting tip

Where it forms: In metasomatic albitite and quartz–muscovite veinlets in an alkaline exocontact surrounding a syenite intrusive. If you start seeing rinkite, zircon, pyrochlore in float, you are in the right ground. Typical habit: platy crystals, granular aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thorbastnäsite?+

Mohs hardness is 4-4.5. Luster: vitreous to greasy. The streak is white. Common colors include brown.

Where is thorbastnäsite found?+

Notable localities include Pichikhol alkaline massif, Balygtyg-Khem River, Sangilen Upland, Tuva, Siberia, Russia.

Is thorbastnäsite safe to handle?+

Thorbastnäsite contains uranium or thorium and calls for real care. Contains thorium, which is radioactive. Handle with care, avoid creating dust, and wash hands thoroughly after contact; store away from other sensitive minerals and living spaces.

What rocks look like thorbastnäsite?+

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

What minerals are found with thorbastnäsite?+

Thorbastnäsite commonly co-occurs with Rinkite, Zircon, Pyrochlore, Euxenite-, Thorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thorbastnäsite form in?+

Where it forms: In metasomatic albitite and quartz–muscovite veinlets in an alkaline exocontact surrounding a syenite intrusive. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thorbastnäsite used for?+

Thorbastnäsite is used in collector.

Find thorbastnäsite on the map

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