Diabase: Description, Characteristics, and Other FAQs

In this article, you’ll obtain answers to common questions about diabase.

What Is Diabase?

Diabase is a dark-colored, fine-grained, igneous rock that consists mostly of plagioclase feldspar and pyroxene.

It forms from the solidification of magma in the Earth’s crust and is thus an intrusive rock. Diabase is also known as dolerite.

What Colors Can Diabase Be?

Diabase can be black, gray, or dark green.

Its fine grain size makes it appear to be aphanitic, or lacking visible grains.

What Is the Composition of Diabase?

As mentioned, diabase consists of plagioclase feldspar and pyroxene.

These minerals make up between 60 and 75 percent of the rock.

The remaining 25 to 40 percent is made up of other minerals, such as olivine, amphibole, and biotite mica.

Where Can Diabase Be Found?

Diabase can be found on every continent.

It’s a very common rock type in North America, Europe, and Africa.

Notable diabase formations can be found in the U.S. states of New Jersey and Pennsylvania, as well as in Scotland, Norway, and South Africa.

What Is Diabase Used For?

Diabase is quarried for a variety of construction purposes, such as crushed stone, dimension stone, and flagstone.

It’s also used to make asphalt and as a railroad ballast.

What Is The Moh’s Hardness Rating of Diabase?

The Moh’s hardness rating of diabase is 6 to 7.

What Type of Rock Is Diabase?

Diabase is an intrusive igneous rock.

Intrusive means that it formed from magma that cooled below the Earth’s surface.

Igneous means that it solidified from molten rock or magma.

In contrast, extrusive means that it solidified on the Earth’s surface, such as from lava.

Is Diabase a Rock or a Mineral?

Diabase is a rock because it consists of an aggregate of minerals.

A mineral is a naturally-occurring, inorganic solid with a definite chemical composition and a crystalline structure. Rocks are made up of one or more minerals.

Therefore, diabase is a rock because it is made up of the minerals plagioclase feldspar and pyroxene.

Is Diabase Valuable?

The value of diabase varies depending on its intended purpose.

For example, dimension stone that is cut and polished for use in countertops or flooring can be quite valuable.

On the other hand, crushed stone that is used as railroad ballast is not very valuable.

Is Diabase Foliated or Non-foliated?

Diabase is non-foliated because it does not have a layered or banded appearance.

Foliated rocks have a layered or banded appearance because they have been subjected to intense pressure, which caused their minerals to realign in parallel layers.

Non-foliated rocks have not been subjected to this type of pressure and do not have a layered appearance.

Is Diabase Felsic or Mafic?

Diabase is mafic because it consists mostly of dark-colored minerals, such as pyroxene and amphibole.

Mafic rocks are typically high in iron and magnesium and low in silicon.

Felsic rocks are the opposite – they are typically high in silicon and low in iron and magnesium.

Is Diabase Aphanitic or Phaneritic?

Diabase is aphanitic because it has an fine-grained or unnoticeable grain size.

Is Diabase Volcanic or Plutonic?

Diabase is plutonic because it cooled below the Earth’s surface.

In contrast, volcanic rocks cooled on the Earth’s surface, such as from lava.

What Is the Density of Diabase?

The density of diabase is 2.7 to 3 grams per cubic centimeter.

What Is the Streak Color of Diabase?

The streak color of diabase is white.

What Is the Luster of Diabase?

The luster of diabase is metallic to dull.

What Is the Cleavage of Diabase?

Diabase has poor cleavage.

What Is the Fracture of Diabase?

Diabase has a conchoidal fracture.

What Is the Crystal System of Diabase?

The crystal system of diabase is monoclinic.

Is Diabase Radioactive?

Diabase is not radioactive.

What Is the Thermal Conductivity of Diabase?

The thermal conductivity of diabase is 2.9 watts per meter Celsius.

Is Diabase Magnetic?

Diabase is not magnetic.

Can Diabase Scratch Scratch Glass?

Yes, diabase can scratch glass.

Diabase is a 6 to 7 on the Moh’s hardness scale, while glass is usually around a 5 to 5.5.

Since diabase is harder, it will scratch glass.

Is Diabase a Sedimentary Rock?

No, diabase is not a sedimentary rock.

Sedimentary rocks form from the accumulation of sediments, such as sand, mud, or organic matter.

In contrast, igneous rocks form from the solidification of molten rock or magma.

Is Diabase Formed From Lava or Magma?

Diabase is formed from magma.

Lava is molten rock that has solidified on the Earth’s surface.

In contrast, magma is molten rock that is still below the Earth’s surface.

Is Diabase Intermediate?

No, diabase is not an intermediate rock.

Intermediate rocks are a type of igneous rock that have a composition that is between mafic and felsic.

Diabase is a mafic rock, which means that it is high in iron and magnesium and low in silicon.

Is Diabase Granite?

No, diabase is not granite.

However, commercially, diabase is marketed as “black granite” though it is not granite from a geological standpoint.

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