Thorite is a radioactive thorium silicate mineral often found in igneous pegmatites. It typically forms square-based prismatic crystals that are frequently metamict, meaning the crystal structure has been damaged by internal radiation over time.
Is this thorite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch thorite with a known reference. Thorite sits at Mohs 4.5-5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light orange to dark brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to resinous or greasy.
- 4Match the color rangeCompare against the expected color range: brownish yellow, brownish black, yellow, dark brown, orange.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: granular, massive, prismatic.
Often confused with
Thorite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Zircon is the harder of the two (Mohs 7.5 vs. 4.5-5); streak differs, so Thorite leaves light orange to dark brown, Zircon leaves white.
How to tell apart: Streak differs, so Thorite leaves light orange to dark brown, Monazite leaves white; luster reads vitreous to resinous or greasy on Thorite and resinous on Monazite.
How to tell apart: Streak differs, so Thorite leaves light orange to dark brown, Allanite leaves gray; luster reads vitreous to resinous or greasy on Thorite and submetallic on Allanite.
Often found alongside thorite
Minerals reported to co-occur with thorite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- ThSiO₄
- Mohs hardness
- 4.5-5
- Density
- 6.63-7.20 g/cm³
- Streak
- Light orange to dark brown
- Luster
- Vitreous to resinous or greasy
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Granular, massive, prismatic
- Cleavage
- {110}, distinct
- Rarity
- Rare
- Uses
- Collector, Ore of thorium
- Host rock
- An accessory mineral in felsic igneous rocks and their associated pegmatites
Where rockhounds find thorite
1 mapped spotsClassic worldwide localities
- Baringer Hill pegmatite, 26 km west of Burnet, Llano Co., Texas, USA
- St. Peters Dome, near Pikes Peak, El Paso Co., and the Powderhorn district, Gunnison Co., Colorado, USA
- Wet Mountains, Custer Co., Colorado, USA
- Lomo, Brevik, and around the Langesundsfjord, Norway
- Arendal, Tvedestrand, Kragerö, Norway
- Mendig, Eifel district, Germany
Field-hunting tip
Where it forms: An accessory mineral in felsic igneous rocks and their associated pegmatites. If you start seeing zircon, monazite, gadolinite in float, you are in the right ground. Typical habit: granular, massive, prismatic. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah. Start trip planning there.
Common questions
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Find thorite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
