Brinrobertsite is a rare sodium potassium calcium hydroxide. It was approved as a distinct mineral species in 1997, from material found at Bangor, North Wales, United Kingdom.

Hardness

1-2

Mohs

Luster

Earthy

Streak

White

Transparency

Transparent

mineralrareSmectite Group family

Brinrobertsite

Brinrobertsite is a rare sodium potassium calcium hydroxide. It was approved as a distinct mineral species in 1997, from material found at Bangor, North Wales, United Kingdom.

Hardness: 1-2
Luster: Earthy
Streak: White
Transparency: Transparent

Is this brinrobertsite?

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 brinrobertsite with a known reference. Brinrobertsite sits at Mohs 1-2, 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: earthy.
4
Match the color range
Compare against the expected color range: gray, yellowish gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: anhedral grains, earthy, microscopic crystals.

Often confused with

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

mineral

Montmorillonite

Mohs 1-2

How to tell apart: Luster reads earthy on Brinrobertsite and dull, earthy on Montmorillonite.

How to tell apart: Luster reads earthy on Brinrobertsite and waxy, resinous, dull on Nontronite.

Compare →

Often found alongside brinrobertsite

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

All properties

Chemical formula: (Na,K,Ca)₀.₃(Al,Fe,Mg)₄(Si,Al)₈O₂₀(OH)₄·3.5H₂O
Mohs hardness: 1-2
Density: 2.4-2.6 g/cm³
Colors: Gray Yellowish gray
Streak: White
Luster: Earthy
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Anhedral grains, earthy, microscopic crystals
Cleavage: Perfect on {001}
Rarity: Rare
Uses: Collector
Host rock: Found in an Ordovician soapy mudtone (metabentonite)

Where rockhounds find brinrobertsite

Classic worldwide localities

Bangor, North Wales, England, Great Britain (type locality)

Field-hunting tip

Where it forms: Found in an Ordovician soapy mudtone (metabentonite). If you start seeing quartz, cerussite, galena in float, you are in the right ground. Typical habit: anhedral grains, earthy, microscopic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify brinrobertsite?+

Mohs hardness is 1-2. Luster: earthy. The streak is white. Common colors include gray, yellowish gray.

Where is brinrobertsite found?+

Notable localities include Bangor, North Wales, England, Great Britain (type locality).

What rocks look like brinrobertsite?+

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

What minerals are found with brinrobertsite?+

Brinrobertsite commonly co-occurs with Quartz, Cerussite, Galena, Chlorargyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does brinrobertsite form in?+

Where it forms: Found in an Ordovician soapy mudtone (metabentonite). Working float back to the host body is the standard way to chase a fresh occurrence.

What is brinrobertsite used for?+

Brinrobertsite is used in collector.

Find brinrobertsite on the map

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