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

Streak

White

Transparency

Opaque

igneouscommon

Basalt

Hardness: 6
Luster: Dull
Streak: White
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
Check the streak
Drag the specimen across an unglazed porcelain plate. Basalt leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Basalt typically shows a dull luster.
4
Match the color range
Compare against the expected color range: black, dark gray, dark green, brown.
5
Look at form & habit
Typical habit: aphanitic to porphyritic.

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
Streak: White
Luster: Dull
Transparency: Opaque
Crystal habit: Aphanitic to Porphyritic
Cleavage: None
Rarity: Common
Uses: Industrial, Construction, Decorative
Host rock: Volcanic Terrains
Typical price: $1-20 for specimens

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

Look in volcanic terrains country, the host setting where basalt typically forms. If you start seeing olivine, plagioclase, pyroxene in float, you are in the right ground. Field specimens usually show a aphanitic to porphyritic habit, so train your eye for that shape before scanning the outcrop. 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. It typically shows a dull luster. The streak is white. 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.

How much is basalt worth?+

Typical asking prices fall in the range of $1-20 for specimens. Quality, size, and provenance can move individual specimens well outside that range.

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?+

Basalt typically forms in 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.