Kentbrooksite is a rare silicate mineral belonging to the eudialyte group, characterized by its distinctive brown coloration and trigonal crystal symmetry. It is primarily found in highly alkaline igneous rocks like those in the Mont Saint-Hilaire region. Collectors prize it as a rare member of the eudialyte family, often occurring as small inclusions or grains within complex pegmatitic matrices.

Hardness

5-6

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrareEudialyte Group family

Kentbrooksite

Hardness: 5-6
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this kentbrooksite?

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 kentbrooksite with a known reference. Kentbrooksite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: yellowish brown.
5
Look at form & habit
Crystal system: trigonal. Typical habit: aggregates, anhedral grains.

Often confused with

Kentbrooksite 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. 5-6).

Compare →

Often found alongside kentbrooksite

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

All properties

Chemical formula: (Na,REE)₁₅(Ca,REE)₆Mn₃Zr₃Nb(Si₂₅O₇₃)(O,OH,H₂O)₃(F,Cl)₂
Mohs hardness: 5-6
Density: 3.10 g/cm³
Colors: Yellowish brown
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Trigonal
Crystal habit: Aggregates, anhedral grains
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In alkaline pegmatitic bodies cutting pulaskite

Where rockhounds find kentbrooksite

Classic worldwide localities

Amdrup Fjord, Kangerdlugssuaq intrustion, East Greenland (type locality)

Field-hunting tip

Where it forms: In alkaline pegmatitic bodies cutting pulaskite. If you start seeing kupletskite, låvenite, catapleiite in float, you are in the right ground. Typical habit: aggregates, anhedral grains. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kentbrooksite?+

Mohs hardness is 5-6. Luster: vitreous. The streak is white. Common colors include yellowish brown.

Where is kentbrooksite found?+

Notable localities include Amdrup Fjord, Kangerdlugssuaq intrustion, East Greenland (type locality).

Is kentbrooksite safe to handle?+

Contains minor radioactive elements; handle with care and wash hands thoroughly after handling. Store away from sleeping or living areas to minimize exposure to long-term radiation.

What rocks look like kentbrooksite?+

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

What minerals are found with kentbrooksite?+

Kentbrooksite commonly co-occurs with Kupletskite, Låvenite, Catapleiite, Hjortdahlite, Eudialyte, Alkali feldspar. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kentbrooksite form in?+

Where it forms: In alkaline pegmatitic bodies cutting pulaskite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kentbrooksite used for?+

Kentbrooksite is used in collector.

Find kentbrooksite on the map

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