Triangulite is an extremely rare uranium-bearing phosphate mineral found in the oxidation zones of granitic pegmatites. It typically occurs as small, delicate, yellowish platy crystals that are difficult to distinguish from other secondary uranium minerals without advanced analytical testing.
Is this triangulite?
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 triangulite with a known reference. Triangulite 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: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow, bright yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: aggregates, rhombohedral crystals, triangular crystals.
Often confused with
Triangulite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Triangulite leaves light yellow, Autunite leaves pale yellow.
How to tell apart: Streak differs, so Triangulite leaves light yellow, Meta-autunite leaves yellow; luster reads vitreous on Triangulite and pearly to dull on Meta-autunite.
Often found alongside triangulite
Minerals reported to co-occur with triangulite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₃(UO₂)₄(PO₄)₄(OH)₅·5H₂O
- Mohs hardness
- 2-3
- Density
- 3.7 g/cm³
- Colors
- Streak
- Light yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Aggregates, rhombohedral crystals, triangular crystals
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary species in the uraniferous oxidized zone of a complex zoned granite pegmatite
Where rockhounds find triangulite
Classic worldwide localities
- Kobokobo pegmatite, Lusungu River district, Kivu Province, Congo (Zaire)
Field-hunting tip
Where it forms: A rare secondary species in the uraniferous oxidized zone of a complex zoned granite pegmatite. If you start seeing meta-autunite, furongite, phosphuranylite in float, you are in the right ground. Typical habit: aggregates, rhombohedral crystals, triangular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify triangulite?+
Where is triangulite found?+
Is triangulite safe to handle?+
What rocks look like triangulite?+
What minerals are found with triangulite?+
What kind of rock does triangulite form in?+
What is triangulite used for?+
Find triangulite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
