Thorianite is a dense, highly radioactive mineral typically found as small cubic or octahedral crystals. It is most commonly sourced from alluvial gem gravels where it occurs as water-worn, heavy black pebbles. Collectors should store this mineral with caution due to its significant radioactive decay properties.
Is this thorianite?
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 thorianite with a known reference. Thorianite 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. Thorianite leaves a grayish-black streak.
- 3Read the lusterHold the specimen under a strong light. Thorianite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-black, reddish-brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: cubes, octahedrons, water-worn pebbles.
Often confused with
Thorianite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Thorianite leaves grayish-black, Uraninite leaves brownish-black to greenish-black; luster reads submetallic on Thorianite and submetallic to dull on Uraninite.
How to tell apart: Streak differs, so Thorianite leaves grayish-black, Zircon leaves white; luster reads submetallic on Thorianite and adamantine on Zircon.
Often found alongside thorianite
Minerals reported to co-occur with thorianite. 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
- Grayish-black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Cubes, Octahedrons, Water-worn Pebbles
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Thorium Source
- Host rock
- Pegmatites, Contact Metamorphic Rocks, Alluvial Deposits
- Typical price
- $50-500 thumbnail depending on size and crystal quality
Where rockhounds find thorianite
Classic worldwide localities
- Sri Lanka
- Madagascar
- Russia
- Canada
Field-hunting tip
Look in pegmatites, contact metamorphic rocks, alluvial deposits country, the host setting where thorianite typically forms. If you start seeing zircon, ilmenite, spinel in float, you are in the right ground. Field specimens usually show a cubes, octahedrons, water-worn pebbles habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify thorianite?+
Where is thorianite found?+
How much is thorianite worth?+
Is thorianite safe to handle?+
What rocks look like thorianite?+
What minerals are found with thorianite?+
What kind of rock does thorianite form in?+
What is thorianite used for?+
Find thorianite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
