Amygdaloidal basalt is a volcanic rock characterized by vesicles that have been filled with secondary minerals. These filled cavities, known as amygdules, often contain high-quality zeolites, agate, or other silicates and are highly prized by collectors.

Hardness

5-6

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

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Amygdaloidal Basalt

Hardness: 5-6
Luster: Dull
Streak: White
Transparency: Opaque

Is this amygdaloidal 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 amygdaloidal basalt with a known reference. Amygdaloidal Basalt sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Amygdaloidal Basalt leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Amygdaloidal Basalt typically shows a dull luster.
4
Match the color range
Compare against the expected color range: gray, black, green, brown.
5
Look at form & habit
Typical habit: massive with spherical to elongated vesicles.

Often found alongside amygdaloidal basalt

Minerals reported to co-occur with amygdaloidal 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: Gray Black Green Brown
Streak: White
Luster: Dull
Transparency: Opaque
Crystal habit: Massive with Spherical to Elongated Vesicles
Cleavage: None
Rarity: Common
Uses: Collector, Geological Study
Host rock: Volcanic Flows
Typical price: $5-50 depending on mineral inclusions

Where rockhounds find amygdaloidal basalt

1 mapped spots

Classic worldwide localities

Lake Superior region, USA
Iceland
Faroe Islands
India
Scotland

Field-hunting tip

Look in volcanic flows country, the host setting where amygdaloidal basalt typically forms. If you start seeing zeolites, quartz, calcite in float, you are in the right ground. Field specimens usually show a massive with spherical to elongated vesicles habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Michigan. Start trip planning there.

Browse 1 U.S. spots for amygdaloidal basalt →

Common questions

How do you identify amygdaloidal basalt?+

Mohs hardness is 5-6. It typically shows a dull luster. The streak is white. Common colors include gray, black, green, brown.

Where is amygdaloidal basalt found?+

Notable localities include Lake Superior region, USA; Iceland; Faroe Islands; India; Scotland.

Can I find amygdaloidal basalt in the United States?+

RockHoundR maps 1 amygdaloidal basalt rockhounding spots across 1 U.S. states. The top states are Michigan.

How much is amygdaloidal basalt worth?+

Typical asking prices fall in the range of $5-50 depending on mineral inclusions. Quality, size, and provenance can move individual specimens well outside that range.

What minerals are found with amygdaloidal basalt?+

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

What kind of rock does amygdaloidal basalt form in?+

Amygdaloidal Basalt typically forms in volcanic flows. Working float back to the host body is the standard way to chase a fresh occurrence.

What is amygdaloidal basalt used for?+

Amygdaloidal Basalt is used in collector, geological study.

Find amygdaloidal basalt on the map

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