Coutinhoite is a rare thorium barium uranium silicate that forms yellow irregular aggregates of curved flaky crystals. It is a secondary hydrothermal mineral in a uraninite-bearing granitic pegmatite. It was first described from Urucum mine, Galiléia Co., Minas Gerais, Brazil.

Hardness

2-3

Mohs

Luster

Waxy to Silky

Streak

Yellow

Transparency

Transparent

mineralrare

Coutinhoite

Hardness: 2-3
Luster: Waxy to Silky
Streak: Yellow
Transparency: Transparent

No image

Is this coutinhoite?

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 coutinhoite with a known reference. Coutinhoite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Coutinhoite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Coutinhoite typically shows a waxy to silky luster.
4
Match the color range
Compare against the expected color range: yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: irregular aggregates of curved flaky crystals.

Often confused with

Coutinhoite 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, so Coutinhoite leaves yellow, Autunite leaves pale yellow; luster reads waxy to silky on Coutinhoite and pearly on Autunite.

How to tell apart: Streak differs, so Coutinhoite leaves yellow, Uranophane leaves yellowish white; luster reads waxy to silky on Coutinhoite and vitreous on Uranophane.

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Often found alongside coutinhoite

Minerals reported to co-occur with coutinhoite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: ThₓBa₁₋₂ₓ(UO₂)₂Si₅O₁₃·3H₂O
Mohs hardness: 2-3
Density: 3.839 g/cm³
Colors: Yellow
Streak: Yellow
Luster: Waxy to Silky
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Irregular Aggregates of Curved Flaky Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites

Where rockhounds find coutinhoite

Classic worldwide localities

Coutinho pegmatite, Minas Gerais, Brazil

Field-hunting tip

Look in granite pegmatites country, the host setting where coutinhoite typically forms. If you start seeing monazite, xenotime, zircon in float, you are in the right ground. Field specimens usually show a irregular aggregates of curved flaky crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify coutinhoite?+

Mohs hardness is 2-3. It typically shows a waxy to silky luster. The streak is yellow. Common colors include yellow.

Where is coutinhoite found?+

Notable localities include Coutinho pegmatite, Minas Gerais, Brazil.

Is coutinhoite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains thorium and uranium and is radioactive; store it apart from other specimens. Wash hands thoroughly after handling and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like coutinhoite?+

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

What minerals are found with coutinhoite?+

Coutinhoite commonly co-occurs with monazite, xenotime, zircon. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does coutinhoite form in?+

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

What is coutinhoite used for?+

Coutinhoite is used in collector.

Find coutinhoite on the map

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