Several Examples of Igneous Rocks

When it comes to igneous rocks we can differentiate them from sedimentary and metamorphic rocks in a couple of ways.  The key difference to note is that Igneous rocks form from the cooling of liquid magma below the earth, or in other cases the cooling of lava on the surface of the earth.  This cooled igneous rock is made up of one or multiple different types of minerals.

Igneous rocks are primarily defined by how they are formed.  For more information on how igneous rocks are formed you may find this article helpful; “How Igneous Rocks are Formed“?

There are many different examples of igneous rocks available on this earth.  Some igneous rocks are more common than others, while others can be quite rare. 

In this article we will list out several of the best examples of igneous rocks with some brief information about them. The examples of igneous rocks we will cover are; Andesite, Basalt, Diorite, Gabbro, Granite, Obsidian, Pegmatite, Peridotite, Pumice, Rhyolite, Scoria, and Tuff.

Some examples of igneous rocks:

Andesite

Andesite is an example of an extrusive igneous rock.  This rock was formed from the cooling of lava on the surface of the earth.  Andesite is a fine grained rock that contains silica and in lower quantities alkali metals such as lithium, sodium, and potassium. 

What makes andesite distinguishable from some of the other igneous rocks similar to it, is the higher content of silicon dioxide in it, at or over 52% (This classifies andesite as “Intermediate”). 

Andesite is typically gray in color and that level of gray will vary depending on the content of hornblende or pyroxene minerals available.  Andesite and diorite are fairly close to the same rock.  Diorite however is the intrusive version of this rock. 

Basalt

Basalt is considered an example of a mafic extrusive igneous rock.  Mafic means that it has roughly 45 to 52% silicon dioxide.  Basalt is high in magnesium and iron and was cooled rapidly on the earth’s surface.  It is said that basalt makes up most of the volcanic rock on earth. 

Planet earth is not the only planet to have basalt available.  Basalt has been determined to be on Venus and Mars, as well as some other places like our moon and the moon ‘lo’, or Jupiter 1, orbiting Jupiter.   Basalt is a darker gray and can often be confused with andesite when it manifests itself as a lighter gray. 

Diorite

Diorite is a great example of an intrusive igneous rock.  This igneous rock forms deep below the earth when the magma cools slowly.  Much like andesite, diorite does have a very distinguishing look of what is called the “salt and pepper” look.  This salt and pepper look can vary from time to time in the rock.  

The dark part, or pepper part, of diorite is what is similar to andesite.  The white, or “salt”, part of the rock will typically be quartz, microcline, and olivine. 

Diorite is often used in counter tops, though people usually refer to it as granite to avoid any confusion.  Diorite is considered to be phaneritic, or having crystals that are big enough to see unaided.  This gives diorite a sparkly appearance when light hits it and can make it quite an attractive rock. For more information on diorite visit this article “All About Diorite” where there is greater detail on this igneous rock.

Gabbro

Gabbro is an example of a mafic intrusive igneous rock.  This igneous rock not extrusive because it slowly cooled beneath the earth. It is however chemically equivalent to basalt, which is cooled above the earth’s surface. 

Gabbro is a very dense rock that can appear to be a bit greenish and dark in color.  This rock is found along the oceanic crust and often can be seen as monolithic mountainous extrusions at times.  Gabbro can be considered a valuable rock as it often contains chromium, nickel, cobalt, gold, silver, platinum, and copper sulfides. 

It is also used at times in counter tops and other structural applications.  Gabbro is commonly known as “black granite”.

Granite

Granite is an igneous rock that consists mainly of quartz, alkali feldspar, and plagioclase.  This common example of an igneous rock forms with high amounts of silica and alkali metal oxides, which makes it felsic. 

Granite comes in many different types.  These types are based on the chemical elements present or amount of those elements present.  Granite can come in many different colors, but the most notable appearance is the orange/pinkish color with the mix of other granular white, gray, or black elements. 

Granite is used in many different building applications such as buildings, benches, streets, monuments and sculptures at times.  Modern day tools have made it much easier to work with granite.  

Obsidian

Obsidian is one of the best examples of an extrusive igneous rock.  Volcanic bursts caused obsidian to cool rapidly on the earth’s surface.  Obsidian is considered to have high viscosity, or greater amount of thickness.  This thick volcanic material, when cooled quickly, will result in a natural glassy look. 

This hard rock is very brittle and will break apart with very sharp edges.  This feature had made it a favorite for tools and weapons in the past.  Obsidian color can vary depending on what impurities may be present.  It can on rare occasions be colorless but expect it to be dark in color. 

Notable colors such as Black, dark brown, and even reddish in appearance can be common.  Two of the most famous forms of obsidian is “snowflake obsidian” and “rainbow obsidian”. For more in depth information about obsidian visit this article: “All About Obsidian“

Pegmatite

Pegmatite is an example of an intrusive igneous rock.  It has a similar silicon based composition as granite with a composition combination of quartz, feldspar, and mica.  The big feature of this great igneous rock example will be in feature of having large intertwined crystal sizes within its contents. 

Pegmatites, as a host rock, can contain rare minerals such as tungsten and titanium, and gemstones such as fluorite and topaz.  This rock will often be mined for the minerals that are contained within them. 

Peridotite

Peridotite is an ultramafic igneous rock example with less than 45% silica content.  It contains mainly olivine and pyroxene.  Peridotite is very high in magnesium due to the olivine content with amounts of iron as well. 

There are four types of peridotite; Dunite, Harzburgite, Lherzolite, and Wehrlite.  One of the key things to note about peridotite is that diamonds and other rare minerals can be present in the rock.  There are some indicators that help to identify these types peridotite such as the presence of garnet, chromite, and ilmenite. 

Peridotite will typically be green in color and be coarsely grained in nature.

Pumice

Pumice is a volcanic igneous rock that has what is called a foamy appearance. This appearance can will look in similar to a sponge or sea coral in many cases.  This igneous rock example has quite a few uses from early type medicines and construction materials, to horticulture and personal hygiene. 

This rock is mined continually for its many uses and being an extrusive igneous rock, you don’t have to dig too deep to acquire it.  Pumice is pale in color and can be white, blue, grey, black, and brownish-green. 

This rock is high in porosity, with a lower than 1 density. This means pumice will float on water for a time depending on how long those pockets of air in the rock don’t get filled.

Rhyolite

Rhyolite is a good example of a felsic extrusive igneous rock. It is known as the most silica abundant of all the volcanic rocks.  This rock is typically a fine grained rock in texture, but can contain larger mineral crystals. 

The makeup of rhyolite is mostly quartz, sanidine, and plagioclase.  Rhyolite is the equivalent of the intrusive granite.  Much like obsidian in its uses, rhyolite carried some similar capabilities that were used in the past when it came to forging weapons and tools. For more information on rhyolite visit this article: “All About Rhyolite“

Scoria

Scoria is a volcanic igneous rock which is dark in color.  This example of igneous rock will typically be a dark brown, black, or a purple red.  This rock is highly pitted with cavities within the rock, making it look like a sponge or coral. 

This particular rock is different than pumice though they may have the same porosity.  Scoria has a specific gravity over 1 and will sink in water.  Scoria will at most times contain glassy looking fragments and can contain preformed hidden crystals within.  Landscaping, high temperature insulation, and drainage applications are some common uses of this rock.

Tuff

Tuff is an example of a volcanic extrusive igneous rock which is made from volcanic ash during an eruption.  With pressure and time, all fluids will be expelled from this rock and solidify to make tuff. 

The rock is considered to be tuff if it is 75% or more volcanic ash.  Tuff is one of those special rocks that can be classified as either igneous or sedimentary rock due to its formation in nature.  This rock is primarily used as a building material for buildings and bridges.