Imogolite is a rare aluminosilicate clay mineral that typically forms as extremely fine, hollow nanotubes in volcanic soils. It is rarely found in macroscopic crystals and is primarily studied for its unique nanostructure and high surface area in geological and materials science.

Hardness

2-3

Mohs

Luster

Vitreous, resinous, waxy

Streak

White

Transparency

Transparent to translucent

mineraluncommonKaolinite-Serpentine Group family

Imogolite

Hardness: 2-3
Luster: Vitreous, resinous, waxy
Streak: White
Transparency: Transparent to translucent

Is this imogolite?

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 imogolite with a known reference. Imogolite 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. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous, resinous, waxy.
4
Match the color range
Compare against the expected color range: yellowish white, light brownish yellow, blue, green, brown.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: earthy.

Often confused with

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

How to tell apart: Luster reads vitreous, resinous, waxy on Imogolite and pearly, waxy, or dull on Halloysite.

Compare →

Often found alongside imogolite

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

All properties

Chemical formula: Al₂SiO₃(OH)₄
Mohs hardness: 2-3
Density: 2.70 g/cm³
Colors: Yellowish whiteLight brownish yellowBlue Green Brown
Streak: White
Luster: Vitreous, resinous, waxy
Transparency: Transparent to translucent
Crystal system: Monoclinic
Crystal habit: Earthy
Cleavage: None
Rarity: Uncommon
Uses: Scientific research, Catalysis
Host rock: In soils derived from volcanic ash

Where rockhounds find imogolite

Classic worldwide localities

Misutsuchi bed, Iijima, Nagano Prefecture, Japan
Kanumatsuchi bed, Kanuma, Tochigi Prefecture, Japan
Uemura, Kumamoto Prefecture, Japan

Field-hunting tip

Where it forms: In soils derived from volcanic ash. If you start seeing allophane, quartz, cristobalite in float, you are in the right ground. Typical habit: earthy. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify imogolite?+

Mohs hardness is 2-3. Luster: vitreous, resinous, waxy. The streak is white. Common colors include yellowish white, light brownish yellow, blue, green.

Where is imogolite found?+

Notable localities include Misutsuchi bed, Iijima, Nagano Prefecture, Japan; Kanumatsuchi bed, Kanuma, Tochigi Prefecture, Japan; Uemura, Kumamoto Prefecture, Japan.

What rocks look like imogolite?+

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

What minerals are found with imogolite?+

Imogolite commonly co-occurs with Allophane, Quartz, Cristobalite, Gibbsite, Vermiculite, Limonite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does imogolite form in?+

Where it forms: In soils derived from volcanic ash. Working float back to the host body is the standard way to chase a fresh occurrence.

What is imogolite used for?+

Imogolite is used in scientific research, catalysis.

Find imogolite on the map

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