Thornasite is a rare sodium thorium silicate, typically colorless to very pale green. It was approved as a distinct mineral species in 1985. It was first described from Mont Saint-Hilaire and near Saint-Amable, Quebec, Canada.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Opaque

mineralrareTerskite Group family

Thornasite

Hardness: 5
Luster: Vitreous
Streak: White
Transparency: Opaque

Is this thornasite?

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 thornasite with a known reference. Thornasite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Thornasite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Thornasite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, pale green, beige.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: tabular crystals, massive, granular.

Often confused with

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

Often found alongside thornasite

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

All properties

Chemical formula: Na₁₂Th₃(Si₈O₁₉)₄·18H₂O
Mohs hardness: 5
Density: 2.62 g/cm³
Colors: Colorless Pale Green Beige
Streak: White
Luster: Vitreous
Transparency: Opaque
Crystal system: Hexagonal
Crystal habit: Tabular Crystals, Massive, Granular
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Agpaitic Syenite Pegmatites

Where rockhounds find thornasite

Classic worldwide localities

Mont Saint-Hilaire, Canada

Field-hunting tip

Look in agpaitic syenite pegmatites country, the host setting where thornasite typically forms. If you start seeing aegirine, microcline, sodalite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thornasite?+

Mohs hardness is 5. It typically shows a vitreous luster. The streak is white. Common colors include colorless, pale green, beige.

Where is thornasite found?+

Notable localities include Mont Saint-Hilaire, Canada.

Is thornasite safe to handle?+

This mineral is radioactive. Contains thorium and is radioactive; store it apart from other specimens. Wash hands thoroughly after handling and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like thornasite?+

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

What minerals are found with thornasite?+

Thornasite commonly co-occurs with Aegirine, Microcline, Sodalite, Nepheline. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thornasite form in?+

Thornasite typically forms in agpaitic syenite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thornasite used for?+

Thornasite is used in collector.

Find thornasite on the map

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