Komatiite is a rare ultramafic volcanic rock characterized by its unique spinifex texture formed by rapid cooling of magnesium-rich lava. It is primarily found in Archean greenstone belts and represents some of the hottest volcanic eruptions in Earth's early history.

Hardness

5-6

Mohs

Luster

Dull

Transparency

Opaque

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Komatiite

Hardness: 5-6
Luster: Dull
Transparency: Opaque

Is this komatiite?

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 komatiite with a known reference. Komatiite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
2
Read the texture
Look at a fresh break with a hand lens. Texture: Often spinifex texture of large dendritic olivine and pyroxene plates.
3
Pick out the minerals
Composition: Forsteritic olivine, calcic pyroxene, anorthite and chromite; at least 18 percent magnesium oxide. Identify the two or three most abundant grains.
4
Read the luster
Hold the specimen under a strong light. Luster: dull.
5
Match the color range
Compare against the expected color range: dark gray, greenish-gray, black.

Often confused with

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

How to tell apart: Luster reads dull on Komatiite and vitreous to dull on Peridotite.

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Often found alongside komatiite

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

All properties

Mohs hardness: 5-6
Density: 2.8-3.3 g/cm³
Colors: Dark gray Greenish-gray Black
Luster: Dull
Transparency: Opaque
Rarity: Rare
Uses: Geological research, Collector
Host rock: Archean volcanic sequences
Texture: Often spinifex texture of large dendritic olivine and pyroxene plates
Composition: Forsteritic olivine, calcic pyroxene, anorthite and chromite; at least 18 percent magnesium oxide

Where rockhounds find komatiite

Classic worldwide localities

Barberton Greenstone Belt, South Africa
Abitibi Greenstone Belt, Canada
Yilgarn Craton, Australia
Finland

Field-hunting tip

Where it forms: Archean volcanic sequences. If you start seeing olivine, pyroxene, chromite in float, you are in the right ground.

Common questions

How do you identify komatiite?+

Mohs hardness is 5-6. Texture: Often spinifex texture of large dendritic olivine and pyroxene plates. Composition: Forsteritic olivine, calcic pyroxene, anorthite and chromite; at least 18 percent magnesium oxide. Luster: dull. Common colors include dark gray, greenish-gray, black.

Where is komatiite found?+

Notable localities include Barberton Greenstone Belt, South Africa; Abitibi Greenstone Belt, Canada; Yilgarn Craton, Australia; Finland.

What rocks look like komatiite?+

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

What minerals are found with komatiite?+

Komatiite commonly co-occurs with olivine, pyroxene, chromite, serpentine. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does komatiite form in?+

Where it forms: Archean volcanic sequences. Working float back to the host body is the standard way to chase a fresh occurrence.

What is komatiite used for?+

Komatiite is used in geological research, collector.

Find komatiite on the map

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