Basalt Rock (Lava Rock)

With volcanic rocks like Scoria being so popular as a vivarium rock, it’s only a matter of time before you run across the word Basalt…

You might even be considering a particular type of stone for an upcoming project.

Rest assured, this article will cover Basalt Rocks in detail and go further into depth as to why an aquarium enthusiast should consider using it in an enclosure.

Quick Stats:
Traditional Name Basalt
Common Names Lava Rock, Basalt Rock
Origin Lava Flow, Igneous Dike
Habitat Islands, Ocean Floors, Volcano Fields
Color Gray, Black, Brown
Density (g/cm3) 3.00g
Hardness 6
PH Impact Neutral (No Effect)
Elemental Type Extrusive Igneous Rock (Mafic)

What Is Basalt Rock?

Basalt is an igneous rock formed from flowing lava that’s cooled when it reaches the earth’s surface.

Much like Scoria, it is an extrusive stone composed of minerals often found in magma like magnesium and iron.

Basalt can also form platonically within the earth’s crust if magma reaches a cooler temperature without an actual volcanic eruption.

Essentially, Scoria and Basalt are very much the same kinds of rock.

The difference between the two is Scoria forms on the outer layer of the cooled magma retaining most of the captured gas while cooling forming vesicular holes throughout the stone.

On the other hand, Basalt is denser and has much fewer, if not any vesicular holes in it.

Scoria is also commonly referred to as “vesicular basalt.”

Lava Rock "Basalt" Aquascape Tips

Basalt Rock Facts

Basalt makes up for about 90% of all Lava Rocks formed across the world.

It is found in nearly all natural soils and is an essential part of all plant life found in nature.

Due to Basalt weathering quicker than rocks that contain minerals like quartz, it can provide necessary nutrients to plants that root in basalt-rich soils much faster.

This is why areas where volcanic activity has occurred always have a thriving flora ecosystem.

Adding Basalt Rocks to a vivarium or scattering dust from this rock in the substrate of indoor plants can have an incredibly positive impact on the plants growing around it.

Many Hobbyists will consider this the natural way to nourish plants compared to using a potting mix.


Basalt is mostly recognized for its dark color and dense solid state.

As I mentioned earlier, it doesn’t usually have many vesicular bubbles formed within it due to most of the gas passing through the cooling magma faster than it can harden.

So the fine-grained minerals that this rock is composed of, form a more solid and smooth textured stone.

Lava Rocks break into fractured patterns, meaning it doesn’t split into multiple layers of thin cleavage plates like Slate Rocks typically do.

It’s common to find Basalt stacked into uniform sets of pillars due to the way it fractures out in nature.

Basalt Rocks that find their way onto ocean floors will even weather into round circular shaped stones.

This is something to consider when using it as a hardscape material in saltwater as well as freshwater aquariums.

The color of Basalt Rocks typically ranges between dark grey and black.

This is due to the concentrated amounts of iron and magnesium found in the lava.

It isn’t uncommon to find Basalt with specs of red or full brownish color as well.

These colors are contributed to rapid oxidation when forming.

The contained iron minerals oxidize when exposed to environmental elements during the cooling phase of the magma.


Basalt is the most abundant type of igneous rock known on our planet.

It makes up most of the underlining layer of the earth’s crust and parts of the ocean floor.

Deep ocean basins are underlain by basalt.

The only way Basalt is naturally found above the earth’s land surface is through the process of volcanic eruptions and lava flows.

Environmental Influence

Basalt is an inert rock that doesn’t have an impact on water parameters.

This makes it a good choice for all aquariums because it will not cause the PH to go up or down.

Furthermore, it won’t have an influence on the water hardness either.

Since Basalt Rock makes up most of the ocean basins underlain, this is a natural choice to use in saltwater tanks.

Freshwater enclosures can benefit exceptionally well when Basalt is used in aquascaping.

Basalt Rocks weather over time much faster than other igneous rocks and in doing so, provide plants with nutrients only found in nature.

Smaller bits of crushed Basalt mixed into the substrates of terrariums will lead to the same positive impact on plants being kept in those types of vivariums as well.

Vivarium Preference

Basalt is well-suited for many types of vivariums.

It does well above ground as well as fully submerged in both hard and soft water conditions.

This makes it a very fitting prospect to use as a hardscape in any type of terrarium or aquarium.

Use larger pieces of Basalt to form hardscape structures that can support wood and plants.

Be mindful that this is a rather dense stone so parts should be firmly placed and not stacked dangerously high.

Smaller pebble size pieces as a substrate or mixed in with soil to provide additional nutrients to the roots of vivarium plants.


As we touched on earlier, Lava Rocks are a very universal and inert rock to experiment with within vivariums.

Basalt is the core ingredient in the majority of Lava Rocks found today making it no exception.

Its rapid weathering characteristics allow a consistent amount of minerals to slowly leech from the stone and be absorbed into local plant roots.

The dark contrast this stone is usually found in also makes it blend nicely into any enclosure.


The downside to Basalt Rocks, when compared to other vivarium rocks, is the weight.

These are some of the denser Lava Rocks averaging around 3 grams per centimeter cubed.

This could mean disaster if not properly managed in a tank.

Most hobbyists prefer lighter-weight rocks to scape with because it’s safer to use around inhabitants in the event of a collapse.

Heavier enclosures also mean more pressure against the walls holding everything together.

The hardness of Basalt can also make it more difficult to work with as well.

This type of Lava Rock scores a hardness level of about 6 making it harder than glass.

The harder the rock is usually a good thing for the most part though once everything is in place and established.

Buy Basalt Rock

Even though Basalt is the most common type of igneous rock found in the world, it has yet to really hit the market for vivarium use like Scoria or Pumice.

This makes it a bit harder to find for sale locally.

You will also have to use your wits and test newly purchased Basalt Rocks for imperfections before placing them in an established tank.

Click the image below to find out more about the current price and other relative info:

Basalt Rock Recommendations

Here are a few more useful tips when working with Basalt for the first time.

Inspect the rocks to see what type of Lava Rock has been acquired.

Based on the color as well as the sturdiness of the stone, you should be able to identify the possible minerals compacted into the formation of this rock.

Before placing any type of Lava Rock in an acidic vivarium, always do a quick alkaline test to assure there are no possibly toxic minerals contained within the rock.

As usual, clean the Basalt Rock to remove access dust or loose particles from the surface.

Cleaning Basalt Rock

In most cases, newly acquired Basalt will need slight preparation before going into a vivarium.

This will matter more for aquariums rather than terrariums since unclean stones can cause water to change color.

Begin by placing stones in a bucket of cold water.

Scrub and redip each stone thoroughly in the bucket of water.

Rinse and repeat this process until you are able to place stones in a clean bucket of water and observe no noticeable change in color.

Avoid using chemicals or strong water pressure on the rocks so they aren’t worn down drastically and lose their aesthetics.

Breaking Basalt Rock

With a hardness score of 6, Basalt can be a bit more difficult to strategically break than most other aquarium rocks.

A chisel and hammer kit will more than likely be required to break the stone up into small parts.

This rock breaks into fracture-type pieces so don’t worry about trying to get the perfect shape.

If an attempt to chisel out cave formations or arches causes the stone to split into undesired parts, simply superglue the rock back together.

Sprinkle specs or loose basalt dust over the newly glued seams to cover unnatural separation.

Rocks Similar To Basalt Rock

When designing a new enclosure for the first time, it would be best to stick with one type of stone to use as a hardscape.

Furthermore, this type of rock can be hard to come by depending on where you are located in the world.

If for any reason, you find Basalt difficult to acquire, or simply want to consider something different…

There are a wide variety of stones to consider.

Here are some other types of stones one might find are worth taking a look at in place of Basalt Rocks:

Marble Rock "Metamorphic Limestone" Hardscape Guide
Pagoda Rock "Sandstone" Hardscape Guide
Limestone "Calcarenite Rock" Hardscape Guide


Basalt Rocks are really great hardscaping stones to use in vivariums.

I personally like using them in combination with other types of Lava Rocks like Scoria to create a custom aquascape that seamlessly flows together.

The dark contrast this rock provides is a nice aesthetic touch to colorful flora.

Basalt is also one of the few vivarium stones that supply nutrients to local plants almost immediately due to its quick weathering.

If you stumbled across this article and never considered Basalt’s use in an enclosure, what are your thoughts towards this type of Lava Rock after reading this post?

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