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 — Thorite leaves dark brown, Zircon leaves white; luster reads resinous on Thorite and adamantine on Zircon.
How to tell apart: Streak differs — Thorite leaves dark brown, Monazite leaves white.
How to tell apart: Streak differs — 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 — that is 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.
