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. Thorite leaves a dark brown streak.
- 3Read the lusterHold the specimen under a strong light. Thorite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: black, brown, orange, yellow.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic crystals.
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 dark brown, Zircon leaves white; luster reads resinous on Thorite and adamantine on Zircon.
How to tell apart: Streak differs, so Thorite leaves dark brown, Monazite leaves white.
How to tell apart: Streak differs, so Thorite leaves dark brown, Allanite leaves gray; luster reads resinous 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
- 4.4-6.6 g/cm³
- Streak
- Dark Brown
- Luster
- Resinous
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic Crystals
- Cleavage
- Distinct On 110
- Rarity
- Rare
- Uses
- Collector, Ore of Thorium
- Host rock
- Igneous Pegmatites and Alkaline Rocks
- Typical price
- $20-200 per specimen
Where rockhounds find thorite
1 mapped spotsClassic worldwide localities
- Langesundsfjord, Norway
- Bancroft, Ontario, Canada
- Colorado, USA
- Madagascar
- Cornwall, England
Field-hunting tip
Look in igneous pegmatites and alkaline rocks country, the host setting where thorite typically forms. If you start seeing zircon, feldspar, quartz in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so 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.
