Basalt is a mafic extrusive igneous rock formed from the rapid cooling of low-viscosity lava flows. It is characteristically dark-colored and fine-grained, often displaying columnar jointing or vesicular textures due to gas bubbles trapped during solidification.

Hardness

Mohs

Luster

Dull

Transparency

Opaque

igneouscommon

Basalt

Hardness: 6
Luster: Dull
Transparency: Opaque

Is this 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 basalt with a known reference. Basalt sits at Mohs 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: Aphanitic. Grain size: Fine-grained.
3
Pick out the minerals
Composition: Plagioclase-dominated feldspar, under 20 percent quartz and under 10 percent feldspathoid; 45 to 52 percent silica. 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, dark green, brown.

Often confused with

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

How to tell apart: Luster reads dull on Basalt and vitreous on Gabbro.

Compare →

Often found alongside basalt

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

All properties

Mohs hardness: 6
Density: 2.8-3.0 g/cm³
Colors: Black Dark gray Dark green Brown
Luster: Dull
Transparency: Opaque
Rarity: Common
Uses: Industrial, Construction, Decorative
Host rock: volcanic terrains
Texture: Aphanitic
Grain size: Fine-grained
Composition: Plagioclase-dominated feldspar, under 20 percent quartz and under 10 percent feldspathoid; 45 to 52 percent silica

Where rockhounds find basalt

9 mapped spots

Classic worldwide localities

Iceland
Hawaii, USA
Giant's Causeway, Northern Ireland
Columbia River Plateau, USA
Deccan Traps, India

Field-hunting tip

Where it forms: volcanic terrains. If you start seeing olivine, plagioclase, pyroxene in float, you are in the right ground. In the U.S., the densest reported localities are in Michigan, Wisconsin, California. Start trip planning there.

Browse 9 U.S. spots for basalt →

Common questions

How do you identify basalt?+

Mohs hardness is 6. Texture: Aphanitic. Composition: Plagioclase-dominated feldspar, under 20 percent quartz and under 10 percent feldspathoid; 45 to 52 percent silica. Luster: dull. Common colors include black, dark gray, dark green, brown.

Where is basalt found?+

Notable localities include Iceland; Hawaii, USA; Giant's Causeway, Northern Ireland; Columbia River Plateau, USA; Deccan Traps, India.

Can I find basalt in the United States?+

RockHoundR maps 9 basalt rockhounding spots across 4 U.S. states. The top states are Michigan, Wisconsin, California.

What rocks look like basalt?+

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

What minerals are found with basalt?+

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

What kind of rock does basalt form in?+

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

What is basalt used for?+

Basalt is used in industrial, construction, decorative.

Find basalt on the map

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