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.

Hardness

2.5-3

Mohs

Luster

Dull

Streak

Yellow

Transparency

Opaque

mineralrare

Triangulite

Hardness: 2.5-3
Luster: Dull
Streak: Yellow
Transparency: Opaque

Is this triangulite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch triangulite with a known reference. Triangulite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Triangulite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Triangulite typically shows a dull luster.
4
Match the color range
Compare against the expected color range: yellow, yellowish-green.
5
Look at form & habit
Crystal system: triclinic. Typical habit: platy crystals.

Often confused with

Triangulite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Autunite

Mohs 2-2.5

How to tell apart: Streak differs — Triangulite leaves yellow, Autunite leaves pale yellow; luster reads dull on Triangulite and pearly on Autunite.

How to tell apart: Luster reads dull on Triangulite and pearly on Meta-autunite.

Compare →

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: Al₄(UO₂)(PO₄)₂(OH)₈·5H₂O
Mohs hardness: 2.5-3
Density: 4.55 g/cm³
Colors: Yellow Yellowish-green
Streak: Yellow
Luster: Dull
Transparency: Opaque
Crystal system: Triclinic
Crystal habit: Platy Crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find triangulite

Classic worldwide localities

Kobokobo pegmatite, Democratic Republic of the Congo

Field-hunting tip

Look in granite pegmatites country — that is the host setting where triangulite typically forms. If you start seeing phosphuranylite, meta-autunite, furongite in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify triangulite?+

Mohs hardness is 2.5-3. It typically shows a dull luster. The streak is yellow. Common colors include yellow, yellowish-green.

Where is triangulite found?+

Notable localities include Kobokobo pegmatite, Democratic Republic of the Congo.

How much is triangulite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is triangulite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains uranium and is significantly radioactive; handle with care, use gloves, and store in a lead-shielded container. Avoid inhalation of dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like triangulite?+

Triangulite is most often confused with Autunite, Meta-autunite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with triangulite?+

Triangulite commonly co-occurs with Phosphuranylite, Meta-autunite, Furongite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does triangulite form in?+

Triangulite typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is triangulite used for?+

Triangulite is used in collector.

Find triangulite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.