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

Classic worldwide localities

Lake Superior region, USA
Iceland
Faroe Islands
India
Scotland

Field-hunting tip

Look in volcanic flows country — that is 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.

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.

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

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