The 3 Different TYPES OF ROCKS (With Examples Of Each!)

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The 3 Different Names Of Rocks...And Examples Of Each Kind Of Rock

Guide to three main types of rocks


Whether you’re an avid rockhound or someone who just loves nature, you notice rocks everywhere. Fact is, you can’t even take the dog for a walk down the street without stepping on them. Rocks are everywhere you look.

And with so many rocks everywhere around us, you may be surprised to learn that there’s really only three different kinds of rocks out there.  I know when I first learned this is kind of blew me away!

So if you’re interested in learning about what those three types of rocks are, as well as learning what some examples of each type of rock are...then keep on reading!

Let's get right to it!

3 Types Of Rocks

different kinds of rocks

In short, there are three different types of rocks that every rock you meet can be classified as.  The three types of rocks are:

  • Igneous Rocks

  • Metamorphic Rocks

  • Sedimentary Rocks

1. Igneous Rocks

The first type of rock on this list are the igneous type of rocks. Igneous rocks are more than just  a cool name. They’re actually cool in another way.

Igneous rocks are actually cooled and hardened magma. That means that Igneous rocks are formed when molten rock from deep within the earth rises to the surface (lava) and cools.  Sometimes the magma will cool inside the earth before it even reaches the surface.

It’s this cooling period that decides what kind of igneous rocks that magma turns into. Because there’s two types of Igneous rocks.  

  • Intrusive
  • Extrusive

Intrusive Igneous Rock

Intrusive igneous rocks form when magma cools slowly thousands of feet below the Earth's surface. Most intrusive rocks have large, well-formed crystals. Examples of intrusive igneous rocks include granite, gabbro, diorite and dunite.

Extrusive Igneous Rock

Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most extrusive (volcanic) rocks have small crystals. Examples of extrusive igneous rocks include basalt, rhyolite, andesite, and obsidian.

Igneous Rocks Examples

Below are a few examples of the most popular types of Igneous rocks. (The descriptions below are from geology.com)

Andesite (Larch Mountain Andesite, Lower Pleistocene, 1.43 Ma; Larch Mountain Shield Volcano, Boring Volcanic Field, Oregon, USA) 1


Andesite - Andesites are simply fine-grained extrusive indigenous rocks that are light gray in color. They consist mainly of plagioclase minerals that are mixed together with hornblende, biotite and pyroxene.

Basalt

Basalt - Basalts are fine-grained volcanic rocks. They are dense and appear in dark-gray color. They mainly consist of plagioclase and pyroxene. Basalts are the most common form of solidified lava and are utilized in building and construction processes.
Pumice Stone

Pumice - Pumice is a very porous and vesicular igneous rock that results from rapid solidification of magma. The porousness and vescularity of its texture is caused by the gas trapped in the molten rock as it undergoes solidification. 
obsidian

Obsidian - Obsidians are dense extrusive igneous rocks that are dark in color. They are created when lava cools rapidly without crystalizing. They are dark, but are clear in slim pieces, and was often times used to make arrowheads by ancient civilizations.
Granite (Silver Plume Granite, Mesoproterozoic, 1.42 Ga; Rt. 36 roadcut, Larimer County, Colorado, USA) 1

Granite - Granite is a coarse-grained intrusive igneous rock that are generally light in color. Granite is composed of three different minerals: mica, feldspar and quartz, and is widely used in construction due to its widespread availability and durability.
Rhyolite

Rhyolite - Rhyolite are fine-grained extrusive igneous rocks that are light in color. They are usually made up of quartz and feldspar minerals. They normally possess a smooth surface. 

2. Sedimentary Rocks

Sedimentary rocks are formed at the surface of the Earth. This can take place either in water or on land. Sedimentary rocks are exactly what they sound like...sediment.

Sedimentary type rocks are layered accumulations of different kinds of sediments, such as fragments of rocks, minerals, and even animal and plant material.

Most sedimentary rocks become cemented together by the minerals and chemicals that they contain.  Sometimes these layers are even held together by electrical attraction. But they’re are also sedimentary rocks that never really fuse together and remain loose.

All of these multiple layers of sedimentary rock generally run parallel (or nearly parallel) to the Earth's surface. But you’ll also notice while out in the field that some of these layers run at high angles, and are not parallel to the earth's surface.  If you see this, then you know that there’s been some kind of major geological movement that moved that layer of rock after it was formed.

As a matter of fact, sedimentary rocks are forming around us all the time.

  • Sand and gravel on beaches or in river bars look like the sandstone and conglomerate that they will eventually become.

  • Compacted and dried mud flats harden into shale.

  • Scuba divers who have seen mud and shells settling on the floors of lagoons find it easy to understand how sedimentary rocks form.

All together, there are three basic types of sedimentary rock:

Clastic sedimentary rocks - such as breccia, conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris.

Chemical sedimentary rocks - such as rock salt, iron ore, chert, flint, some dolomites, and some limestones, form when dissolved minerals precipitate from solution.

Organic sedimentary rocks - such as coal, some dolomites, and some limestones, form from the accumulation of plant or animal debris.

Sedimentary Rocks Examples

Below are a few examples of the most popular types of sedimentary rocks. (Info below is from eartheclipse.com)

Breccia

Brecia - Brecia are clastic sedimentary rocks made up of angular rock broken parts that are cemented together. The broken pieces are similar to conglomerate because of their large pea-sizes. Breccias are commonly found along fault zones and they take any color.
Quartz-pebble conglomerate (Upper Paleozoic; Salt Creek gravel bar clast, Haynes, Ohio, USA) 2

Conglomerate - Conglomerates are clastic sedimentary rocks composed of semi-rounded rock fragments that are cemented together.  Conglomerate fragments are commonly deposited along the shoreline or stream channel and they are pea-sized or larger. They’re also referred to as pudding stone.

Sandstone

Sandstone - Sandstones are clastic sedimentary rocks that are made up of sand grains that have been cemented together. Sandstones vary from fine-grained to coarse grained are readily distinguishable by the naked eyes. Mature sandstones or quartz sandstones are light-colored and majorly consist of rounded and well-sorted quartz grains.

Black shale
Shale - Shale consists of clay minerals or clay-sized pieces that have been compacted by the weight of the overlying rock. Shale belongs to clastic sedimentary rocks and they tend to split into fairly flat pieces. They are generally a good source of fossils and are mostly found at the bottom of lakes or oceans.
Brachiopod fossils in weathered limestone (Upper Mercer Limestone, Middle Pennsylvanian; Rock Cut railroad cut, south-southeast of Dresden, Ohio, USA) 3

Limestone - Limestones are chemical sedimentary rocks made up of the mineral calcite and can be difficult t​​​​o identify visually. Common types of limestone include fossiliferous limestone which is great for containing fossils.

Ferruginous chert ("jasper")
Chert - Cherts are chemical sedimentary rocks formed due to the deposition of cryptocrystalline quartz. Cherts are of dull brown or gray in color and are often found as nodules firmly enclosed in limestone which protrude out of the limestone when the limestone is slowly immersed in water. Jasper can be red, bright yellowish brown or reddish brown chert.


3. Metamorphic Rocks

Finally, Metamorphic rocks. What are they? Well, sometimes the other two types of rocks, sedimentary and igneous rocks, can be under such high pressures or intense heat so high that the rocks actually “morph”, or change. These changes rocks become metamorphic rocks.

This change to metamorphic rock takes place very deep within the earth's crust. The process of this change does not melt the rocks like you would think, but instead what it does is literally transform them into rocks that are more dense and compact.

Metamorphic Rocks Examples

Below are a few examples of the most popular types of metamorphic rocks. (Info below is from rocksandminerals4u.com)

Quartzite 4
Quartzite - Quartzite is a coarse-grained metamorphic rock derived from sandstone. Heat and pressure combine to fuse grains of quartz sand that make up the composition of quartzite.
Blue calcitic marble (proximal host rock to the Valentine wollastonite skarn deposit, late Mesoproterozoic, 1130-1160 Ma; Valentine Mine (Gouverneur Talc Company No. 4 Quarry), Lewis County, New York State, USA)
Marble - Marble is a metamorphic rock that comes from metamorphosed limestone or dolomite. It can be most any color including white, black, reds, greens, and more and is used as building materials for its strength and beauty.
Slate (Knife Lake Formation, metamorphism at 2.7 Ga, Neoarchean; Rt. 135 roadcut, Gilbert, Minnesota, USA) 7
Slate - Slate is a fined grained metamorphic rock. Shale is the parent rock. It is made up of clay minerals.
Muscovite schist (Paleoproterozoic; Black Hills, South Dakota, USA) 3
Schist -Schist is a coarse grained metamorphic rock and shale is the parent rock. If you look at a piece of this metamorphic rock on the right you may be able to see crystals of the minerals that make up the rock.
Gneiss (Joshimath Formation, Proterozoic; outcrop at Joshimath, Uttarakhand State, Indian Himalayas) 2
Gneiss - is a medium to course grained metamorphic rock. Shale is the typical parent rock. It is made up of clay minerals. Shale can metamorphose into slate, phyllite, schist or gneiss depending on the degree of heat and pressure.


Conclusion

So there you have it...all three different types of rocks with a few examples of each kind. So what kind of rock do you have in your collections.  Which kind do you have near by your favorite rock collecting site.  

I hope this helped provide a little insight and understanding into the different types of rocks that we rockhounds love so much.  

As always, if you have any questions, don't hesitate to leave a comment below or shoot me a message!

Happy rockhounding!


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3 Main Types Of Rocks (VIDEO)