Thorite is a primary source of the element thorium and is found primarily in igneous environments like pegmatites. It is highly radioactive and often contains inclusions of uranium or iron, resulting in its dark, metallic appearance. Collectors should prioritize safe storage practices due to its significant radiation output.
Is this thorium?
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 thorium with a known reference. Thorium sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Thorium leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Thorium typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: lead-gray, black, brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: massive, cubic crystals.
Often confused with
Thorium vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Thorium leaves black, Uraninite leaves brownish-black to greenish-black; luster reads submetallic on Thorium and submetallic to dull on Uraninite.
How to tell apart: Streak differs — Thorium leaves black, Zircon leaves white; luster reads submetallic on Thorium and adamantine on Zircon.
Often found alongside thorium
Minerals reported to co-occur with thorium. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- ThO₂
- Mohs hardness
- 6.5-7
- Density
- 9.0-10.0 g/cm³
- Streak
- Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive, Cubic Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Ore Mineral, Collector
- Host rock
- Pegmatites, Granites, Alluvial Sands
- Typical price
- $20-200 per specimen
Where rockhounds find thorium
1 mapped spotsClassic worldwide localities
- Madagascar
- Canada
- Brazil
- Norway
- USA
Field-hunting tip
Look in pegmatites, granites, alluvial sands country — that is the host setting where thorium typically forms. If you start seeing monazite, zircon, uraninite in float, you are in the right ground. Field specimens usually show a massive, cubic 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 thorium on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
