Vesicular basalt is an extrusive igneous rock characterized by numerous small cavities called vesicles, formed by gas bubbles trapped in cooling lava. These cavities are often later filled by secondary minerals like zeolites, quartz, or calcite, making them popular targets for micromounters and collectors.

Hardness

5-6

Mohs

Luster

Dull

Transparency

Opaque

igneouscommon

Vesicular Basalt

Hardness: 5-6
Luster: Dull
Transparency: Opaque

Is this vesicular basalt?

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 vesicular basalt with a known reference. Vesicular Basalt 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: Pitted with many cavities (vesicles) left by trapped gas bubbles. Grain size: Fine-grained (aphanitic).
3
Pick out the minerals
Composition: Basalt. 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: black, dark gray, brownish-gray.

Often confused with

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

Often found alongside vesicular basalt

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

All properties

Mohs hardness: 5-6
Density: 2.8-3.0 g/cm³
Colors: Black Dark gray Brownish-gray
Luster: Dull
Transparency: Opaque
Rarity: Common
Uses: Decorative, Landscaping, Collector
Host rock: volcanic surface flows
Texture: Pitted with many cavities (vesicles) left by trapped gas bubbles
Grain size: Fine-grained (aphanitic)
Composition: Basalt

Where rockhounds find vesicular basalt

Classic worldwide localities

Hawaii, USA
Iceland
Etna, Italy
Columbia River Plateau, USA

Field-hunting tip

Where it forms: volcanic surface flows. If you start seeing olivine, plagioclase, zeolites in float, you are in the right ground.

Common questions

How do you identify vesicular basalt?+

Mohs hardness is 5-6. Texture: Pitted with many cavities (vesicles) left by trapped gas bubbles. Composition: Basalt. Luster: dull. Common colors include black, dark gray, brownish-gray.

Where is vesicular basalt found?+

Notable localities include Hawaii, USA; Iceland; Etna, Italy; Columbia River Plateau, USA.

What rocks look like vesicular basalt?+

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

What minerals are found with vesicular basalt?+

Vesicular Basalt commonly co-occurs with Olivine, Plagioclase, Zeolites, Calcite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does vesicular basalt form in?+

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

What is vesicular basalt used for?+

Vesicular Basalt is used in decorative, landscaping, collector.

Find vesicular basalt on the map

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