Thorogummite is a thorium-rich silicate mineral that typically forms as an alteration product or pseudomorph of thorite. It appears as dull, earthy, and often brownish masses, making it visually distinct from the more lustrous, unaltered thorite crystals.
Is this thorogummite?
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 thorogummite with a known reference. Thorogummite sits at Mohs 4-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Thorogummite leaves a light brown streak.
- 3Read the lusterHold the specimen under a strong light. Thorogummite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: yellowish-brown, brown, grayish-brown, black.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: massive, earthy, pseudomorphs after thorite.
Often confused with
Thorogummite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Thorogummite leaves light brown, Thorite leaves dark brown; luster reads dull on Thorogummite and resinous on Thorite.
How to tell apart: Zircon is the harder of the two (Mohs 7.5 vs. 4-5); streak differs — Thorogummite leaves light brown, Zircon leaves white; luster reads dull on Thorogummite and adamantine on Zircon.
How to tell apart: Streak differs — Thorogummite leaves light brown, Monazite leaves white; luster reads dull on Thorogummite and resinous on Monazite.
Often found alongside thorogummite
Minerals reported to co-occur with thorogummite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Th(SiO₄)₁₋ₓ(OH)₄ₓ
- Mohs hardness
- 4-5
- Density
- 4.4-5.4 g/cm³
- Streak
- Light Brown
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Massive, Earthy, Pseudomorphs After Thorite
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $20-150 thumbnail
Where rockhounds find thorogummite
1 mapped spotsClassic worldwide localities
- Llano County, Texas, USA
- Norway
- Madagascar
- Canada
Field-hunting tip
Look in granite pegmatites country — that is the host setting where thorogummite typically forms. If you start seeing quartz, microcline, biotite in float, you are in the right ground. Field specimens usually show a massive, earthy, pseudomorphs after thorite habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Maine — start trip planning there.
Common questions
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Find thorogummite on the map
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