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 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: brown, greenish gray, buff, white, black.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: massive.
Often confused with
Thorogummite 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. 5.5); streak differs, so Thorogummite leaves light brown, Zircon leaves white.
How to tell apart: Streak differs, so Thorogummite leaves light brown, Monazite leaves white; luster reads vitreous to 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
- 5.5
- Density
- 5.4 g/cm³
- Colors
- Streak
- Light brown
- Luster
- Vitreous to dull
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- granite pegmatites
Where rockhounds find thorogummite
1 mapped spotsClassic worldwide localities
- Llano County, Texas, USA (type locality)
Field-hunting tip
Where it forms: granite pegmatites. If you start seeing quartz, microcline, biotite in float, you are in the right ground. Typical habit: massive. 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
How do you identify thorogummite?+
Where is thorogummite found?+
Can I find thorogummite in the United States?+
Is thorogummite safe to handle?+
What rocks look like thorogummite?+
What minerals are found with thorogummite?+
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Find thorogummite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
