Basalt vs Obsidian: What Are They, And What’s The Difference?

This article discusses the similarities and differences between basalt and obsidian.

Continue reading to learn more about these two igneous rocks.

Basalt vs Obsidian: Summary

Basalt and obsidian are two common igneous rocks known for their dark colors and moderately similar appearances.

These rocks are commonly confused for each other, but they are very different physically and chemically.

Basalt comprises roughly 90% of the world’s volcanic rock, making most people assume all volcanic rock is basaltic.

Obsidian is glass-like and lustrous, much different than dull basalt.

What is Basalt?

Basalt is a dark, fine-grained volcanic rock that forms from the cooling of magma.

Basalt is low in silica but iron and magnesium-rich.

This igneous rock consists of more than 90 percent of the world’s volcanic rock.

Basalt is such a common rock that you can find it in many other areas of our solar system.

It is normal for basalt to display a porphyritic structure with larger crystals.

Basalt can have porous openings, or it can have a dull appearance.

In both cases, it will lack any luster.

Most basalt is black or grey, but it can also be red, orange, or green, depending on the chemical composition.

The most common place to find this rock is underwater fissure eruptions.

You may also find basalt in oceanic hotspots.

What is Obsidian?

Obsidian is a natural glass that forms by the rapid cooling of magma.

It is slightly harder than window glass and sometimes called volcanic glass because of how this rock forms.

Obsidian is typically black, but the rocks’ various minerals can change the color.

It is extremely silica-rich, comprised of between 65 and 80 percent silica, which can change the color dramatically.

In addition, the different cooling temperatures can create unique patterns.

Similarities Between Basalt and Obsidian

People sometimes mistake obsidian and basalt because they have many similarities.

The two rocks have a similar appearance (sometimes) and even come from the same volcanic sources.

Despite having little of the same chemical components, basalt and obsidian have very similar colors.

Both rocks are black, without any hint of other colors unless they have dried inconsistently or have a high amount of a mineral in the magma.

Rock Type

Obsidian and basalt are both volcanic rocks, also called igneous rocks, that form after the cooling of magma.

In some cases, you might gather obsidian and basalt from similar regions.

However, they are not gathered from the same areas of a volcano since they form from different magma types.

Even though the two rocks form from different parts of volcanic magma, they are still the same type of rock. 

Dark Color

Basalt and obsidian have a dark color.

These rocks are typically dark grey or black and can easily be mistaken for each other because of their similar appearance.

Mistaking their appearance most commonly happens from afar, given the luster cannot be seen.

Differences Between Basalt in Obsidian

Basalt and obsidian have many differences, like their luster (shininess) and texture.

From afar, the two rocks might look oddly similar.

However, looking at them closely, you can tell obsidian and basalt are not the same.

Physical characteristics like the texture and luster are key differences between basalt and obsidian. 

Differences between basalt and obsidian are not exclusive to physical characteristics.

The chemical components of basalt and obsidian are different too.


The textures of basalt and obsidian are different.

Obsidian is angular and sharp, with cracks.

Basalt appears soft, with softer edges and a smooth surface.

The interior of basalt looks the same as the exterior.

The natural glass obsidian can be black or multi-colored on the inside. 


The luster of basalt and obsidian differ significantly because of their different cooling processes.

Obsidian cools quickly, creating a shiny exterior.

Basalt cools slowly, creating a matte finish.

The composition of these rocks can impact how quickly they dry.

Chemical Composition

A major difference between the two rocks is their chemical composition.

The two rocks do not look the same because they contain different minerals.

Obsidian is a silica-rich mineral with a glass-like texture and appearance.

Basalt is lower in silica, affecting its appearance, like the texture, luster, color, and more.

Why People Confuse Basalt and Obsidian

People commonly confuse basalt and obsidian because these rocks have similar appearances and origins.

Both igneous rocks form as lava cools, often leading to these rocks forming in the same areas.

You must identify the differences between the two not to confuse the two rocks. 

Furthermore, people often confuse basalt and obsidian because they are untrained to identify the differences.

Since basalt is a more popular rock than obsidian, you might be more inclined to assume the rocks you find near a volcano are basalt.

It is not uncommon to find porous volcanic rocks near a volcano.

However, not all rocks that you find will be basalt.

Similar Appearance

They are similar in appearance from afar.

Both rocks are dark grey or black on the exterior, despite having different textures.

People often mistake these rocks because they are so similar in their appearance.


The two volcanic rocks, basalt and obsidian, are often found in the same areas, making it easy to confuse them despite their differing appearances.

Geologists work hard to identify the correct rocks.

However, the untrained eye can easily categorize the two rocks because they found the rock in the same place. 

Wrap Up

The igneous rocks, obsidian, and basalt are often confused because of their similar appearances and origins.

Since both rocks form because of volcanic eruptions, they are similar in color and can easily be mistaken for each other.

The major difference between these two rocks is the luster of the rocks.

Obsidian is typically shinier than basalt, which has a matte finish instead.

It is common for people to mistake these two rocks because they do not know better.

Basalt makes up most of the world’s volcanic rock supply and is often one of the only volcanic rocks people see.

Grouping two igneous rocks together is a common mistake because obsidian is less popular.

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