30 Types of Rock: How to Identify Each

Written by Drew Wood
Updated: September 25, 2023
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There are over 5,000 known types of minerals. Just a few minerals make up most of the rocks we see, though: feldspars, amphiboles, quartz, olivine, garnet, micas, calcite, and pyroxenes. The possible combinations of these minerals are endless. Rocks also differ based on how they were formed. Igneous rocks form out of cooling lava or magma. Sedimentary rocks develop from eroded grains of other rocks and organic matter. Metamorphic rocks are the third main classification. These started out as other types of rock but were changed by high heat and pressure. In this article, we’ll list 30 types of rock with pictures and a brief description to help you identify them.

1. Andesite

Andesite is a gray or brown extrusive igneous rock. The name comes from the Andes Mountains, where there are abundant deposits of andesite. It makes a good material for construction, landscaping, and other decorative purposes.

Andesite stone

Andesite is abundant in the Andes Mountains.

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©Yes058 Montree Nanta/Shutterstock.com

2. Anthracite

Anthracite is a high-quality form of coal that is hard, pure, and has a slight metallic sheen. It is composed of 86-97% carbon, the highest carbon content of any form of coal. Flames from burning anthracite are short, blue, and smokeless. Anthracite is considered a metamorphic rock.

Atop a coal waste pile at an abandoned anthracite coal mine in Pennsylvania. A wind farm is in the background.

©The American Explorer/Shutterstock.com

Anthracite is the highest grade of coal. It has a high energy content and few impurities.

3. Basalt

Basalt is an extrusive igneous rock, which means it forms from cooling lava on the earth’s surface, not from magma inside the earth. It’s the type of rock Hawaii, the ocean floor, and much of the Moon are made of. It is made of feldspar, olivine, amphibole, and pyroxene. You can identify it from its reddish brown to black color and small holes where gas escaped while the lava was still hot.

Basalt lava rock surface, dark colored structure from lava flow, differnet shades of grey

Basalt is formed from cooling lava on the earth’s surface.

©Iva photos/Shutterstock.com

4. Breccia

Breccia is a kind of sedimentary rock made of sharp, angular fragments of rock and gravel. Piles of rubble that consolidate into breccia can be formed in different ways. Rock may fracture and accumulate at the bottom of cliffs, in areas where volcanoes have erupted explosively, in places where fluid fractures a mass of rock, or as a result of a meteor impact. Breccia is classified as “poorly sorted” or “well sorted” based on whether the rock fragments are different sizes or about the same size.

The presence of volcanic breccias reflects the occurence of gold mineralisation in the oxide zone.

Breccia is sedimentary rock formed from loose broken fragments of other rocks.

©faqihalfyan/Shutterstock.com

5. Chert

Chert is a type of sedimentary rock made of quartz crystals. It usually looks like a chunk of sediment with some smooth, waxy-looking surfaces. It fractures easily, leaving sharp edges. In color, chert is usually brown, grey, or shades of red or green. Sometimes it is translucent, but most kinds of chert are opaque.

Chert, made of quartz crystals, can have red and green shades of color.

©Yes058 Montree Nanta/Shutterstock.com

6. Dacite

This is an igneous rock composed mainly of silica but also has a low percentage of alkali metal oxides. The two most common minerals in dacite are plagioclase feldspar and quartz. Builders can use dacite in projects that require loose aggregate stone. They don’t mix it with concrete, though, as its silica content reacts poorly with concrete.

macro shooting of natural mineral rock specimen - rough Dacite stone on white marble background

Dacite is used as a loose aggregate stone in construction or landscaping projects.

©vvoe/Shutterstock.com

7. Diorite

Diorite is a rock made of white plagioclase feldspar and black hornblende. This creates a black-and-white color. Diorite is similar to granite, but one way to tell the difference is that true diorite does not have quartz crystals in it as granite does. Rock hounds often call rocks “diorite” that are technically something else. Something that looks like diorite but does have quartz crystals in it may be quartz diorite or tonalite. If it has more alkali feldspar than normal diorite, it is called monzonite.

True diorite is relatively uncommon. Many similar-looking rocks have higher quartz or feldspar content than diorite.

©Shutter Wolf/Shutterstock.com

8. Dolostone

Dolostone is a sedimentary rock formed from dolomite and fossils. Over time it can metamorphose into marble. It’s recognizable as a grey rock with visible fossils that are often the same color as the rock it is embedded in.

Ostracods fossilized in dolostone from the Silurian of Ohio, USA.

This sample of dolostone includes fossilized ostracods (small crustaceans) from the Silurian Era.

©James St. John / Flickr – License

9. Eclogite

Eclogite rocks can be igneous or metamorphic. They crystallize out of basaltic magma under high pressure inside the earth. They are made mainly of green pyroxene and red garnet with traces of other minerals like rutile. Sometimes they’re initially mistaken for meteorites because they have a similar composition and are often found as foreign inclusions in other rock layers.

Eclogite, a metamorphic rock

Eclogite has characteristics comparable to meteorites, but it forms in the earth’s mantle.

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10. Gneiss

This type of rock has alternating light and dark bands made of quartz, mica, and feldspar. It is a metamorphic rock made of granite and gabbro. Gneiss forms only when the original rocks are subjected to the high temperatures and pressures that only occur 25 miles beneath the earth’s surface!

Gneiss, a metamorphic rock

Gneiss, a metamorphic rock, forms in the earth at a depth of 25 miles or more.

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11. Granite

Granite is an intrusive igneous rock, forming when magma cools slowly and forms large crystals. The minerals found in granite are feldspar, hornblend, mica, and quartz. You’ll notice crystals of pink feldspar, black mica, and white or grey quartz in granite samples.

Grainte Rock - Types of Igneous Rocks

Granite is a durable and beautiful material often used for construction purposes.

©michal812/Shutterstock.com

12. Ignimbrite

Like rhyodacite, ignimbrite is a rock that forms in pyroclastic flows. It forms out of ash and fragments of pumice, glass, and crystal. Ignimbrite comes in an assortment of colors depending on the exact composition of the sample. Some of the typical colors it comes in are black, grey, white, beige, pink, or brown.

Ignimbrite from Gran Canaria

©www.sandatlas.org/Shutterstock.com

13. Limestone

This common sedimentary rock consists mainly of calcite. It is off-white to grey and has a chalky texture. It can form when calcite precipitates out of seawater and settles on the ocean floor. Another way it forms is from the shells and skeletons of aquatic animals.

Limestone isolated on white background. Limestone is a sedimentary rock composed of skeletal fragments of marine organisms.

Limestone can form from the shells and bones of marine animals, but it does not have visible fossils in it.

©Aleksandr Pobedimskiy/Shutterstock.com

14. Marble

Builders and sculptors from ancient times to the present have favored marble for high-value projects. This is both because it is easy to carve and because of its beautiful coloration. It’s made of light-colored calcite crystals that come in many different shades and has a slight sparkle. Marble is a metamorphic rock formed from limestone or dolostone.

Marble statue at the Vatican

A marble statue at the Vatican

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15. Obsidian

Obsidian is one of the most beautiful and interesting extrusive igneous rocks. It cools from volcanic lava so quickly that it doesn’t have time to form large crystals. The result is smooth black volcanic glass. It is as sharp as glass, too. Shards chipped from made weapons, utility knives, and even surgical-grade medical instruments for premodern people.

Obsidian arrowhead

Obsidian breaks with sharp edges, making it perfect for creating sharp-edged tools such as knives and arrowheads.

©Dima Moroz/Shutterstock.com

16. Peridotite

Peridotite is rich in olivine, pyroxene, magnesium, and iron. This makes it a lot denser than most other types of rock. It’s a common part of the ocean bed and is the main type of rock in the upper mantle. Peridotite is classically colored bright green with specks of black but specimens can change color when weathered or have other mineral traces that make them appear yellow, blue, brown, or red.

©Tyler Boyes/Shutterstock.com

17. Perlite

Perlite is a form of volcanic glass that forms out of hydrated obsidian. When heated up to a high temperature, perlite expands up to 16 times larger and turns bright white. It’s a low-density and inexpensive material that has many different commercial and industrial uses. A few examples of these are: swimming pool filtration, as an additive to agricultural soil, as a component of insulation, ceramics, and explosives, in cosmetics, and in biotechnology applications.

Perlite for indoor potted plants

One common use of perlite is as an additive to potting soil to help with drainage.

©iStock.com/CemSelvi

18. Phonolite

Phonolite is an uncommon extrusive igneous rock. Its most interesting characteristic is that when it is struck with a hammer, it sounds metallic. This is why one of its common names is “clinkstone.” Similarly, the ancient Greeks called it “sounding stone.”

Phonolitic (phonolite) dome of La Catedral (The Cathedral) in the Teide National Park, Tenerife, Canary Islands.

La Catedral (The Cathedral) is a dome of phonolitic rock in the Canary Islands.

©Santi Rodriguez/Shutterstock.com

19. Pumice

Pumice is an igneous rock that forms when gas-filled lava cools quickly. As the gas escapes, it leaves behind a rock as full of holes as Swiss cheese. Its density is less than water, so it can float on the surface of the ocean before it gets completely waterlogged and sinks. Pumice is valuable as an ingredient of abrasive cleaners and sandpaper.

Pumice - Types of Igneous Rocks

One of the most surprising features of pumice is that it is light enough to float on water.

©KrimKate/Shutterstock.com

20. Quartzite

Quartzite is a metamorphic rock formed out of recrystallized quartz grains in sandstone. It is a hard stone that is used as a raw material for glass and ceramics. It’s a light grey or white stone with a medium-grained texture.

Quartzite

Manufacturers use quartzite as a key component of glass and ceramics.

©

21. Rhyodacite

Rhyodacite forms when lava in pyroclastic flows cools quickly and forms rocks rich in silica and low in alkali metal oxides. It consists of anywhere from 20-60% quartz. Some of the commercial uses of rhyodacite are in landscaping, as road aggregate, and even for cemetery markers.

Riodacit stone (Rhyodacite) with black background

One use of rhyodacite is as a stone for cemetery grave markers.

©ARadoman/Shutterstock.com

22. Rhyolite

Rhyolite is an extrusive igneous rock. The minerals forming it are hornblend, mica, quartz, and feldspar. It has a fine-grained texture and is pinkish-grey. Sometimes it has dark streaks. Pumice and obsidian are two forms of rhyolite.

Rhyolite on white background.

Rhyolite is a volcanic rock with a fine-grained texture.

©Yes058 Montree Nanta/Shutterstock.com

23. Sandstone

Sandstone is a common sedimentary rock that consists mainly of feldspar or quartz. As other rocks erode, rivers deposit grains of sand from them in areas where the water is moving more slowly. Over time, deep layers of these deposits, fused together by clay, solidify into layers of rock. Sandstone is most commonly tan or grey, but when other minerals are present it can have other colors.

Man on Boat in Arizona

These red cliffs at Lake Powell, Arizona, are sandstone. The red color comes from iron oxide (rust).

©kavram/Shutterstock.com

24. Scoria

This type of rock forms from gobs of lava thrown into the air by a volcano. It cools in the air on the way to the ground, leaving behind a rock full of holes from escaping gas bubbles. Although it is similar to pumice, the big difference is that scoria is denser than water and will immediately sink. Scoria is useful as a material for concrete and the production of cinder blocks.

Scoria pebbles

Scoria is the result of basaltic magma that contains lots of dissolved gas.

©edwsg/Shutterstock.com

25. Serpentinite

Serpentinite is a metaphoric rock. The main mineral components of it are antigorite, lizardite, and/or chrysotile. It is popular as a gemstone or decorative stone because of its deep green color layered with lighter bands in mesmerizing patterns.

Serpentinite

When highly polished, serpentinite makes an attractive stone for ornamental purposes.

©

26. Shale

Shale is a sedimentary rock formed from grains of clay. Its color is brown with a dull red tinge to it and it has very fine grains. Shale is a very soft stone that forms in layers that will easily split apart and crumble in your hands. It will leave muddy streaks if you dip it in water and try to make a mark with it on another surface.

Eternal Flames Falls

This waterfall in western New York flows over stacked layers of shale.

©Jay Ondreicka/Shutterstock.com

27. Slate

In the days before modern technology, you could find slate chalkboards in every classroom and bookbag. That use has faded with time but slate is still used by builders as a flooring and roofing material. It’s a metamorphic rock made of clay minerals. It forms in the heat and pressure found at about 6 miles deep in the earth. You can sometimes guess where a sample might be from based on its color. Various regions produce shale of gray, green, black, red, or even purple.

Shiny slate rock isolated on white background

Depending on where it is mined, slate can come in a number of different colors, including green.

©

28. Syenite

Feldspar is the main mineral in syenite and forms the lighter part of the rock. Other minerals, particularly hornblende, form the dark spots in it. Syenite cools slowly underground, so it has time to form large crystals.

An unpolished syenite rock

Syenite forms along subduction zones, where one tectonic plate is moving underneath another.

©KrimKate/Shutterstock.com

29. Trachyte

Trachyte forms when volcanic lava made of silica and alkali metals cools down rapidly. It is a fine-grained stone that comes in a variety of light colors. Because of its beauty and durability, it is a popular decorative construction material.

closeup of sample of natural mineral from geological collection - unpolished Trachyte rock isolated on white background

Trachyte makes a beautiful construction material.

©vvoe/Shutterstock.com

30. Tuff

Tuff is an igneous rock that forms when compacted volcanic ash solidifies. It is softer than many other kinds of rock, so it is easy to cut into building blocks. The Romans used it as a primary construction materials for their roads, aqueducts, and public buildings.

Easter island

Ancient residents of Easter Island used volcanic tuff to build these enigmatic

moai.

©f11photo/Shutterstock.com

How Many Kinds of Rocks Are There?

Geologists estimate anywhere from 4,500 to 5,000 types of rock are available to people on or near the Earth’s surface. Obviously, our random list of 30 barely scratches the surface. It does give you a taste, though, of the wide variety of rocks that form under different conditions. And you can see a few of the thousands of uses many of these rocks have for construction, agriculture, manufacturing, and decoration. Now, how many of those thousands of rocks can you find?

The photo featured at the top of this post is © Fokin Oleg/Shutterstock.com


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About the Author

Drew Wood is a writer at A-Z Animals focusing on mammals, geography, and world cultures. Drew has worked in research and writing for over 20 years and holds a Masters in Foreign Affairs (1992) and a Doctorate in Religion (2009). A resident of Nebraska, Drew enjoys Brazilian jiu-jitsu, movies, and being an emotional support human to four dogs.

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