Outforia Quicktake: Key Takeaways
- There are three main types of rocks: igneous, sedimentary, and metamorphic.
- Igneous rocks are formed when magma or lava cools, and can be intrusive (cooling within the Earth’s crust) or extrusive (cooling on the surface or seafloor). Examples include basalt and granite.
- Sedimentary rocks are formed through the accumulation and compaction of minerals or organic materials, such as sand or mud. Examples include sandstones and breccias.
- Metamorphic rocks are formed when an existing rock is subjected to high temperatures or pressures, and can originate from igneous, sedimentary, or other metamorphic rocks. Examples include schist and gneiss.
- The rock cycle is a natural process that illustrates the constant transformation of rocks over geologic time, driven by forces like plate tectonics and erosion.
- Minerals are inorganic compounds with distinct chemical structures, while rocks are solid masses containing minerals and other compounds; a rock can consist of multiple minerals or just one, which is called a mono-mineralic rock.
Wherever you go in this world, rocks are sure to abound. Rocks are our firm footing on this planet Earth, and without them, our home would be a vastly different place.
But, not all rocks are the same. In fact, there are hundreds of different rock varieties each of which has its own unique features and properties.
While it’s not possible to name every single rock on Earth, it is possible to impress your friends with your rocky knowledge.
In this article, we’ll introduce you to 30 types of rocks that you ought to know. From shiny obsidian to gorgeous lapis lazuli, here are some of the most amazing types of rocks on the planet that you shouldn’t take for granite. (Okay, we promise—we’ll stop with the rock puns.)
30 Types of Rocks Common on Earth
From andesite to quartzite and everything in between, here’s your ultimate list of the 30 coolest types of rocks on Earth:
Made almost entirely out of plagioclase feldspar, anorthosite is one of the Earth’s most fascinating rocks. However, the most fascinating thing about it is totally out of this world. In fact, anorthosite is one of the oldest rocks found on the surface of the Moon!
Yep, that’s right—in addition to comprising the bulk of the High Peaks area in the Adirondack Mountains of upstate New York, and various parts of the Canadian Shield, anorthosite is found in large quantities on the Moon.
What’s interesting about anorthosite is that geologists still aren’t completely in agreement about how this rock forms. Of course, it’s an intrusive igneous rock, but it’s unclear why anorthosite forms with such high concentrations of plagioclase feldspar.
One of the most visually attractive types of rock, obsidian is a jet-black and smooth rock that’s long played an important role in human culture.
Also called volcanic glass, obsidian is a type of extrusive igneous rock that forms when felsic lavas from a volcano cool very quickly once exposed to the atmosphere. As a result of this rapid cooling, the lava has little time to form crystals, which is why obsidian has such a smooth texture.
Obsidian is found around the world in places such as the United States, New Zealand, Papua New Guinea, Georgia, and Azerbaijan. It has a long track record of being used by human cultures to create arrowheads and other chipped tools. Many Aztec communities also used obsidian to create mirrors, many of which were used for religious and spiritual ceremonies.
Named for French geologist Déodat Gratet de Dolomieu, dolomite is one of the most iconic rock types of the Italian Alps. Found extensively throughout the mountain range that bears its name (the Dolomites), dolomite, or dolostone, is a type of sedimentary rock that mostly consists of the mineral dolomite.
In many ways, dolomite is very similar to limestone as they are both formed from the collection and compaction of calcium carbonate in warm, shallow ocean basins. However, it’s believed that dolomite forms when calcite interacts with magnesium-rich groundwaters.
Either way, dolomite is arguably most famous for the fact that the dolomite-rich mountains of the Dolomites turn spectacular colors at sunrise and sunset. This phenomenon is called enrosadira in Ladin, which is the language of the Ladin people, an ethnic group of the Dolomites. As a result of this phenomenon, the Dolomites turn stunning pink and violet at sunset—a must-see!
- Learn about hundreds of rocks, minerals, crystals, and gems forged by powerful events in prehistory
- Use the book to identify rocks and minerals and open up a new world of discovery
- Discover which rocks fluoresce, which mineral once poisoned an emperor, and which gems are the rarest in the world
- Features a beautiful cover with special effects and hundreds of sharp, reproduced photos of geological specimens
- Written by experienced editor Miranda Smith and teacher/author Sean Callery
- Perfect for young rock hounds and those interested in the natural world.
Basalt is arguably one of the most common rock types on the planet. It is a fine-grained igneous rock that’s known for its stunning dark color. Basalt is mostly composed of pyroxene and plagioclase, and it forms extrusively from lava flows above the Earth’s surface.
One of the reasons that basalt is so abundant is that it underlies the bulk of the ocean basins on Earth. While it isn’t as common on continental plates, basalts comprise the majority of oceanic plates and they are even actively being formed at divergent oceanic boundaries and at oceanic hotspots.
What’s more, basalt is also a particularly abundant rock on the surface of the Moon. We can also find basalt on Mars, particularly around Olympus Mons, which is the planet’s primary shield volcano.
Although it’s gained popularity in recent years for use as a high-end kitchen countertop, granite is so much more than a decorative rock. In fact, granite is a type of intrusive igneous rock that features large feldspar and quartz crystals. Some granites also contain micas and amphiboles that provide them with extra color and uniqueness.
Granite is arguably the most widely known igneous rock on the planet because it is so common. It is particularly prized by rock climbers because granite is a durable rock that creates fascinating topographic features. For example, most of the notable formations in Yosemite Valley, such as El Capitan, consist of granites.
While basalt is the most common type of rock in oceanic crust, granite is likely the most common rock type in continental crust. It often forms in large batholiths or shields as a result of magma that cools under the Earth’s surface.
Crafted out of consolidated volcanic ash, tuff is a bit of a geological oddity. Since it comes from volcanic ash, some biologists consider it to be an igneous rock. However, since tuff consists of consolidated sediments, it could actually be described as a sedimentary rock, too.
Regardless of how you classify it, however, tuff has long been a popular rock for construction. The people of Rapa Nui (Easter Island) actually used it to create the moai, which are the island’s famous human-like statues.
However, keep in mind that there are many different types of tuff, each of which forms from volcanoes with different types of dominant lavas. For example, rhyolite tufts are common in New Zealand while basaltic tufts are more common in Scotland, Iceland, and the Faroe Islands.
Famous for its gorgeous folded bands, gneiss is a type of foliated metamorphic rock that often forms along the edges of convergent plate boundaries. Gneiss undergoes high-grade regional metamorphism during its formation, which is one of the reasons why it has such distinct mineral bands.
The underlying rock that forms gneiss can vary. Common rock types include shale, which can transform first into slate then into both phyllite and schist before becoming gneiss.
Interestingly, unlike many other types of rock, gneiss is not defined by its specific mineral composition. While many gneisses do have quartz and feldspar, gneiss is defined by its bands, which indicate how the rock formed.
Deceptively lightweight, pumice is an extrusive igneous rock that features large gas bubbles.
It forms when lava that has a high water and gas content cools after being discharged from a volcano. As the lava cools, it forms tiny gas bubbles, which is why pumice stones are often much lighter in weight than you’d expect.
Most pumice is lightly colored as it contains a high silica content. It is mined fairly heavily around the world as it is a popular material in construction. Additionally, pumice is used to create various abrasives, such as rubber erasers, or even absorbent materials like cat litter.
You can also buy pumice stones for personal healthcare. That’s because pumice has long been used to help remove calluses from the skin, thanks to its abrasive properties.
Breccia (pronounced bre-CHE-a) is a funky type of sedimentary rock that’s actually composed of broken fragments of other rocks that get cemented together by compression.
It is very similar to conglomerates in that it’s effectively an amalgamation of other rocks. However, breccia is distinct from conglomerates as a conglomerate must consist of rounded fragments of rock while breccia must consist of angular fragments.
Breccia’s fragments can be metamorphic, igneous, or sedimentary in origin, though breccia is considered to be a sedimentary rock. It has long been used by humans for decorative purposes and it can be seen in building columns that date back thousands of years.
More commonly referred to as just “coal,” anthracite is considered to be the highest quality coal on the planet. It is a highly compacted type of coal that’s been heavily metamorphosed and contains upwards of 98 percent carbon.
Because anthracite has such a high concentration of carbon, it provides the highest energy density of any other coal type, including bituminous, subbituminous, and lignite coal. As such, it has historically been used to create electricity.
However, like all fossil fuels, the burning of anthracite has disastrous effects on our climate. It can also have serious health effects for people who work in coal mines as breathing in coal dust over the long term can cause coal workers’ pneumoconiosis (black lung).
Boasting large crystals, schist is a fascinating type of metamorphic rock that’s famous for sometimes containing large garnets.
Schist often forms at convergent plate boundaries. It’s created through the mid-grade metamorphism of sedimentary rocks, such as shales and mudstones. As such, it often has large concentrations of mica, hornblende, quartz, and feldspar.
But, arguably the most famous characteristic of schist is that it can’t feature large garnet gems. These gorgeous gems can come in nearly any color, though red is the most common. They can be quite large and they have long been used as gemstones due to their fantastically rich colors.
12. Lapis Lazuli
Easily the most captivating rock on our list, lapis lazuli is a type of metamorphic rock that forms in a deep blue coloration. It is considered to be a semi-precious stone thanks to its amazing colors, and it has been considered to be valuable to humans for thousands of years.
In general, lapis lazuli forms near igneous intrusions through contact metamorphism. It is most commonly found in Afghanistan, but there are other areas around the world that also produce lapis lazuli in decently large quantities.
Although lapis lazuli is too soft to be used in rings, it is often used to create pendants and earrings. It needs to be heavily polished in order to be gemstone quality, but its gorgeous blue colorations are hard to beat.
One of the world’s rarest rocks, llanite is a type of stunning extrusive igneous rock. Technically it can be classed as a type for rhyolite, but llanite is only found in one area of Llano County, Texas.
What makes llanite unique is that it features a unique blend of highly distinctive blue quartz crystals that are mixed with perthitic feldspar. Blue quartz on its own is quite rare and it gives llanite a visual appeal that you can’t get anywhere else.
Considered to be a type of breccia, suevite is a unique rock that’s also known as an “impactite.” Impactites are any rock that forms as a result of an impact event, such as a meteor strike.
Although not much is known about suevite, it’s believed that it forms when surrounding rock is heated to extremely high temperatures as a result of the pressure of the impact event that it metals and then cools very rapidly. This rapid melting and cooling forms various glasses and other crystals.
What’s unique about suevite is that it’s actually an amalgamation of angular fragments of these crystals and glasses. It’s often used by geologists as a “diagnostic rock,” which means that it’s used to identify true impact craters.
Another fairly common type of rock, andesite is an extrusive igneous rock that’s often considered to be an intermediate between darkly colored basalts and lightly colored rhyolites.
Andesite gets its name from the Andes mountains in South America, which is one of the world’s longest mountain ranges. The rock is common in the range because it is created through the rapid cooling of andesitic lavas that are produced by volcanoes in the region.
Additionally, andesite is fairly common at convergent plate boundaries, especially as oceanic crust subducts under continental crust. It’s also been found on two meteorites that landed in the Graves Nunataks region of Antarctica.
The second semi-precious stone on our list, unakite is a type of gemstone that features stunning green and pink colorations. It is a coarse-grained rock that undergoes metamorphosis, which helps to showcase its stunning pistachio-green epidote and pink orthoclase minerals.
Unakite is a popular material in jewelry, sculpting, and construction. It is commonly used because it is fairly inexpensive. However, it is also easy to work with and it adds fantastic colors to any structure. In fact, unakite is found on the front steps of Washington, D.C.’s Smithsonian National Museum of Natural History.
Oh, and the name unakite comes from the Unaka Mountains, which are a subrange of the Blue Ridge Mountains that stretch along the border between Tennessee and North Carolina in the southeastern United States.
Amphibolite is a peculiar type of metamorphic rock that traditionally forms along convergent plate boundaries. It’s named after amphibole, which is one of its primary minerals. Amphibole comes in a variety of colors though green is arguably what it’s best known for.
Other major minerals in amphibolite include plagioclase feldspar and hornblende. However, it contains minimal, if any quartz, which is one of the reasons why it is so darkly colored.
Amphibolite has long been used by humans for tool making. In fact, it has been found in adzes, which are a type of cutting tool, that date back to the Neolithic. It’s also a fairly common stone used in paving and in buildings because of its great hardness and aesthetic.
Sometimes called calcrete or kankar, caliche is a fascinating type of sedimentary rock. It is effectively a natural cement that’s comprised of calcium carbonate, sands, silts, gravels, and clays.
As a general rule, caliche is lightly colored, but there are some darker colored caliches out there. It is found throughout the world in arid or semi-arid regions, such as the Mojave Desert.
One of the things that makes caliche so unique is that it is very hard to dig through. While many sedimentary rocks aren’t very difficult to break, caliche’s natural cement can make it a problem during construction projects. Caliche is also fairly impermeable, so it can cause issues for farmers if it causes the soil to drain poorly, which can flood crops.
A truly amazing type of limestone, coquina is a sedimentary rock that’s noted for its unique aesthetic properties.
What’s unique about coquina is that it is predominately, if not entirely, composed of the shells of trilobites, invertebrates, or mollusks. In fact, the name coquina comes from a Spanish word that means “cockle,” which is a type of mollusk.
These rocks form, as you might suspect, in shallow seas, through the accumulation of various shells. As a result of its composition, coquina has a rough, yet captivating, texture that has made it popular for use in building in some coastal areas.
Scoria is a type of igneous rock that’s known for its many bubble-like air holes. It is almost always very dark in color, but it can be a bit lighter in color if it’s formed from andesitic lava.
This type of rock forms when lava with large quantities of dissolved gasses is released from a volcano during an eruption. As a result of these dissolved gasses, the scoria develops tiny air bubbles.
Scoria is most commonly associated with cinder cones, which are a type of volcano. However, do note that it is not the same as pumice as scoria is usually made from basaltic lavas while pumice usually comes from rhyolitic lavas.
One of the most popular building and sculpting materials, marble is a metamorphic rock that’s prized for its aesthetic qualities.
Marble forms through the metamorphism of limestones or dolostones. Due to this metamorphism, the carbonate crystals in limestones or dolostones get recrystallized into an interlocking mosaic.
While pure marble is technically completely white, most marbles have various veins and swirls. These veins and swirls are the result of impurities, which may include chert, sand, silt, or iron oxides. There are also some green colorations that you can see in certain marbles, which are the result of serpentines.
Among the lesser-known rocks in this list, skarn is a metamorphic rock that often forms near the edges of large bodies of magma.
It forms through a unique process called metasomatism, which is when rocks are metamorphosed through contact with hot, chemically active fluids. The majority of skarns originate as carbonate rocks, which include marbles, dolomites, and limestones.
Skarns often contain large garnets as well as other gems, such as sapphires and rubies. Sometimes, skarns can contain deposits of lead, tin, copper, zinc, tungsten, molybdenum, and even gold.
Chert is a sedimentary rock that’s been used by humans as a tool or building material since time immemorial. It is mostly comprised of quartz and it can also form through the petrification of wood.
Many cherts are white or black in color, but you can find cherts in nearly any color imaginable. Usually, the color of chert is a result of the trace elements found in the rock itself, with some reddish cherts containing trace amounts of oxidized iron.
As is the case with obsidian, chert has been used for centuries as a material to create arrowheads and other tools. Technically, flint is a type of chert that has long been used to make tools.
Another incredibly useful rock, soapstone has been mined by humans for millennia for both decorative and utilitarian purposes.
Soapstone is defined as a metamorphic rock that consists mostly of talc. It may have various amphiboles, carbonates, chlorites, and pyroxenes, as well as micas, but soapstone must have talc to be considered a soapstone.
The primary benefit of soapstone is that it is non-absorbent and easy to carve. Soapstone has been mined by humans nearly everywhere it is found, including in Ancient Egypt and in India. It is also featured prominently on the outer layers of Rio de Janeiro’s Christ the Redeemer statue
Although some geologists consider mariposite to be a mineral, it can also be classified as a rock. Mariposite is actually an informal name that’s used to refer to a collection of metamorphic rocks that contain large amounts of green micas.
As you can imagine, these green micas give these rocks a unique coloration, which makes them a particularly beautiful material to build with.
The name mariposite comes from the community of Mariposa in California. It was a prized sight during the California Gold Rush as many miners realized that mariposite rocks often contained sizable amounts of gold. However, the rock is found elsewhere, particularly in the US state of Washington and on the island of Newfoundland in Canada.
26. Oil Shale
Oil shale is a type of sedimentary rock that, as its name suggests, contains large amounts of liquid hydrocarbons (a.k.a. oil). There are sizable deposits of oil shale around the world, particularly in the western United States, Australia, Brazil, and parts of Europe.
As you can imagine, oil shale is a prized resource in the fossil fuel industry because it can produce valuable oil. However, it is generally fairly expensive to extract oil from oil shales, to say nothing of the environmental impact of burning oil.
Additionally, the mining of oil shale also has negative environmental impacts. It’s known to cause widespread water pollution in regions where it’s mined, often because it causes heavy metals, like mercury, to leach into surface water.
Found in batholiths along mid-ocean ridges and in ancient mountain ranges, gabbro is a darkly colored type of intrusive igneous rock.
It forms through the very slow cooling of magma that’s rich in irons and magnesium, which allow it to create large crystals. Technically, gabbro is the intrusive equivalent of basalt if you look at each rock’s classic chemical composition.
The name gabbro comes from that of a village that’s located in the Italian region of Tuscany. It was first noted in the scientific literature in the eighteenth century in the Italian Apennines, but it is found around the world, including in the famous Black Cuillin range on the Isle of Skye in Scotland.
Also known as diatomaceous earth, diatomite is a type of sedimentary rock that consists nearly entirely of silica. It has been used by humans at least as far back as the time of the Ancient Greeks as it is prized for its almost pure white color.
Diatomite is made from the fossilized remains of diatoms, which are a group of microalgae. It is found all over the world, including in Poland, Germany, the United States, Denmark, and Scotland.
Although diatomite has been used by humans for millennia, it is now a popular compound used to create everything from air filters to abrasives. It was most famously used by Alfred Nobel to stabilize nitroglycerin to create his ground-breaking dynamite (okay, this time we mean it—no more rock puns!).
An extremely common rock type, quartzite is a metamorphic rock that’s almost exclusively made from quartz.
It generally forms whenever sandstones that are rich in quartz minerals are metamorphosed by heat and pressure. This metamorphism causes the grains of the sandstone to recrystallize, which gives the resulting quartzite superhero-like strength.
Quartzite is now a popular tool for everything from countertops to construction because it is so hard and durable. It’s also substantially cheaper than both granite and marble, so it’s better for use in many regards to some more traditional stones. There are also manufactured quartzites available that are even more durable for use in countertops.
Last but not least, we have hornfels, which is technically the name for a group of rocks that are formed through contact metamorphism. This means that they form through exposure to extreme heat, which causes the crystals in the original rock to re-align.
Hornfels is usually created from various sedimentary rocks, such as limestone, sandstone, and shale. Unlike these original rocks, however, hornfels is very hard and durable.
Traditionally, hornfels was also used in England to create whetstones due to its great durability. But do note that most modern natural whetstones are actually quartz-based rocks like novaculite.
How Are Rocks Classified?
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Now that you’re familiar with 30 amazing types of rock, let’s talk a bit about how rocks are actually classified.
Throughout this article, we’ve mentioned various rock classifications, such as igneous, metamorphic, and sedimentary. These three rock types are considered to be the general classes of rock because they group together rocks based on their origin.
Although there’s enough information about the classification of rocks to fill multiple books, the idea is that there are three primary ways that rocks form.
Igneous rocks are created when magma or lava cool. They can be intrusive, which means that the magma cools in the Earth’s crust, or extrusive, which means that lava cooled on the surface of the Earth or on the seafloor. Examples include basalt and granite.
Metamorphic rocks form when an existing rock is subjected to very high temperatures or very high pressures. The original rock can be igneous, sedimentary, or even metamorphic in origin. Examples include schist and gneiss.
Sedimentary rocks form through the accumulation and compaction of minerals or organic materials. This is most common in shallow seas, but it can happen anywhere. Examples include sandstones and breccias.
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The Rock Cycle
Each of the three main types of rock that we described above (igneous, sedimentary, and metamorphic) goes through transitions over time.
For example, an igneous rock can erode away into sediments that become a sedimentary rock some millions of years later. Eventually, if that same sedimentary rock is subjected to high heat and pressure, it is how metamorphic rocks formed.
In this way, the rocks on Earth are all part of something called the rock cycle. Much like the water cycle, the rock cycle is a natural process that occurs throughout geologic time. There are a number of forces that drive the rock cycle including plate tectonics and erosion.
The key idea here is that the rock cycle effectively acts like a recycling system for rocks. Since the Law of Conservation of Mass tells us that matter cannot be created or destroyed, all the rocks on Earth have existed on Earth since the planet formed (except those that arrived by meteor, of course).
Therefore, the rocks that you see on our planet today have likely undergone multiple transformations in their lifetimes. They may have started as igneous rocks but they may have been metamorphosed into a metamorphic rock, then eroded and compacted into sedimentary rock, and then subducted and melted, where they then formed igneous rocks once again.
While it may take a very, very long time for this to happen, the rock cycle reminds us that geologic time is now and that the world around us is constantly changing.
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Types of Rocks FAQs
Here are our answers to some of your most commonly asked questions about rocks:
What Are The 3 Rock Types?
The 3 basic rock types are igneous, sedimentary, and metamorphic. Igneous rocks form through the cooling of magma or lava while sedimentary rocks are compacted collections of sediment, such as sand or mud. Finally, metamorphic rocks are any rock that’s been subjected to intense heat and/or pressure.
Is A Mineral Considered A Rock?
Minerals and rocks are technically different things. A mineral is an inorganic compound with a distinct chemical structure. Rocks are solid masses that consist of minerals and other compounds. A rock can contain multiple minerals or just a single mineral. A rock that contains just one mineral can be called a mono-mineralic rock.