Threadgoldite is a rare uranyl phosphate mineral characterized by its bright yellow, thin platy crystals that resemble mica. It is primarily found as a secondary mineral in the oxidized zones of uranium deposits and requires careful handling due to its radioactivity.
Is this threadgoldite?
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 threadgoldite with a known reference. Threadgoldite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: greenish yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: micaceous, tabular.
Often confused with
Threadgoldite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside threadgoldite
Minerals reported to co-occur with threadgoldite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al(UO₂)₂(PO₄)₂(OH)·8H₂O
- Mohs hardness
- 2-3
- Density
- 3.4 g/cm³
- Colors
- Streak
- Yellow white
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Micaceous, tabular
- Cleavage
- On {100}, micaceous; also on {001}, {010}, {012}
- Fluorescence
- Pale green under SW UV; green under LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in the uraniferous zone of a complex zoned granite pegmatite
Where rockhounds find threadgoldite
Classic worldwide localities
- Found in the Kobokobo pegmatite, Lusungu River district, Kivu Province, Congo (Zaire)
- South Alligator Valley, Northern Territories, Australia
Field-hunting tip
Where it forms: A rare secondary mineral in the uraniferous zone of a complex zoned granite pegmatite. If you start seeing meta-autunite, phosphuranylite, phuralumite in float, you are in the right ground. Typical habit: micaceous, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify threadgoldite?+
Where is threadgoldite found?+
Is threadgoldite safe to handle?+
What rocks look like threadgoldite?+
What minerals are found with threadgoldite?+
What kind of rock does threadgoldite form in?+
What is threadgoldite used for?+
Find threadgoldite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
