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What is Sandstone? Types, Properties, and Formation

Joseph Comunale, Sheila Morrissey
  • Author
    Joseph Comunale

    Joseph Comunale obtained a Bachelor's in Philosophy from UCF before becoming a high school science teacher for five years. He has taught Earth-Space Science and Integrated Science at a Title 1 School in Florida and has Professional Teacher's Certification for Earth-Space Science.

  • Instructor
    Sheila Morrissey

    Sheila has a master's degree in geology and has taught middle school through university-level science courses.

Learn about sandstone and what type of rock is sandstone. Learn if sandstone is a sedimentary rock, how sandstone is formed, and what minerals are in sandstone. Updated: 11/09/2021

What is Sandstone?

Over vast spans of geological time, the Earth's crust changes by moving, deforming, weathering, and eroding. It moves and deforms by being uplifted and subducted by the tectonic forces within Earth's interior. Earth's atmosphere, biosphere, and hydrosphere then work on the rocks that make up Earth's crust, physically and chemically weathering rock and breaking it down into sediments. These sediments erode or are transferred to new locations where they are deposited and accumulate. Some sediments can eventually reform into rock-like sandstone. But what is sandstone? And is sandstone a sedimentary rock?

Sandstone is a type of clastic sedimentary rock composed of sand, hence its name. However, there are many different kinds of sand and, therefore, different kinds of sandstone. A rock is only classified as sandstone if the sediments that compose it are silicate grains between 0.0625 and 2 millimeters (i.e., sand).

Sandstone Formation

Rocks are continually recycled, typically on timescales of millions of years, in what's known as the rock cycle. The three major types of rocks - igneous, metamorphic, and sedimentary - can each be turned into a new metamorphic rock when given enough heat and pressure. Each rock type can be turned into a new igneous rock if it is completely melted and then cooled again. Sedimentary rocks are made when other rocks are broken into fragments and those fragments are cemented together to form a new rock. One of the most common types of sedimentary rock is sandstone.

As the name implies, sandstone contains sand-sized grains of rock fragments and individual minerals broken down from other, older rocks. We all have a sense of how big sand grains typically are from our experience going to the beach or playing in a sand box. Geologists also know that sand-sized grains have a particular measurement, from about 1/16th of a millimeter to 2 millimeters.

We say source rocks, the original rocks that eventually make up the small grains of a sandstone, are weathered when they break down. The pieces coming off a source rock can then be eroded, or carried away from the source area. The longer the chunks of a source rock are carried by wind, water, or ice, the more likely they are to be broken down into very small fragments. Certain minerals found within rocks are also more likely to survive significantly long rock fragment travels. Because quartz is such a hardy mineral, unlikely to undergo chemical changes during erosion, it is the mineral found in the greatest amounts in many sands. On most beaches (and of course there are exceptions), you will find a lot of hard, almost clear-looking grains of sand, which are most likely quartz.

After a source rock is weathered and eroded, the resulting sand grains might fill a bowl-shaped basin on land or underwater. With the pressure from more sediments landing above and the movement of water through the grains, the sand becomes sandstone. Finer grains of rock and new mineral growth fill the spaces between the grains, cementing the new rock.

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This image shows sedimentary rock layers at Zabriskie Point in Death Valley.

Is sandstone clastic, is sandstone a sedimentary rock. The answer is yes. Sedimentary rock is seen in this image.

What Type of Rock is Sandstone?

As previously mentioned, sandstone is a clastic sedimentary rock. Sedimentary rocks are rocks formed from the accumulation of deposited sediments that undergo a process of cementation to bind them into a rock. Sandstone is a sedimentary rock composed of sand sediments that were fragmented from pre-existing rocks and minerals through physical weathering actions such as wind, gravity, and flowing water. Sandstone is a clastic rock because its sediments were broken down through physical processes rather than chemical processes. But how is sandstone made?

This image shows a sandstone formation at Valley of Fire State Park. This formation definitely meets the sandstone description.

What is sandstone or what type of rock is sandstone can be answered by understanding its composition. This image shows sandstone.

How Is Sandstone Formed?

The sand grains and sediments that form sandstone firstly originate from pre-existing rock. These pre-existing rocks undergo physical weathering before being transported and accumulating in a new location. Lastly, the sediments must be compacted and cemented to result in sandstone.

Weathering & Transportation of Source Rock Material

The pre-existing rock that breaks down into sediments that eventually forms sandstone is called the source rock. The source rock provides the source material that form sandstone. The processes that break down rocks to form clastic materials are physical weathering processes. A rock can be physically broken down in several ways. The most basic ways a source rock can break down is through abrasive processes such as rock tumbling down the side of a mountain due to gravity or sandblasting (wind picking up other sediments that then impact the source rock).

Additionally, water can play a huge role in breaking down a rock. Flowing water can cause rocks to impact each other and result in abrasion. Water can also accumulate in the cracks of rocks before freezing and expanding in the winter. As water freezes, it expands, which results in ice wedging where the expanding ice widens the cracks of a rock every winter before the rock fragments completely.

After a source rock is physically weathered and fragmented, the particles or sediments that result are transported through the process of erosion. Sediments can be eroded or transported chiefly by wind and flowing water.

Deposition of Sediment

After clastic sediments are picked up by wind or flowing water and transported, they are eventually deposited in new locations. As the wind or water slows down or bends around corners, sediments also lose their momentum and can come to a stop; this is common in meandering rivers, for example. Meandering rivers or rivers that turn and bend produce both erosion and deposition. Faster flowing water in a river impacts source rock and sediment on the outside of a bend or meander. The outer edge of a river bend, therefore, erodes. Water flowing on the inside of a bend is moves more slowly and deposits sediments and sand on the inside edge of the river bend.

This sandstone is found in Switzerland and is composed of alternating grey fluviatile sandstone deposited by a meandering river sometime in the distant past.

Where does sandstone form and how is sandstone made. This sandstone formed from a meandering river.

Compaction and Cementation

After sand grains and sediments are deposited at a new location, sediments can continue to accumulate, resulting in the compaction of the buried sediments. This process can occur underwater or on land. As more and more sand grains accumulate and compact the sediments beneath them, a matrix material can be introduced to the system by something like water. Where the sand grains make up the framework of the sandstone rock, the matrix material is a finer-grained sediment that contributes to the cementation of the framework. As finer-grained sediments (matrix material) work into the compacted sand, cement begins to form. Cementation produces cement or new mineral growth between the framework sand grains through the accumulation of the matrix sediment. The new mineral growth between the compacted sand grains then binds the sand, forming the clastic sedimentary rock known as sandstone.

Sandstone is a common sedimentary rock and comprises approximately 20-25% of all sedimentary rocks. But where does sandstone form? And how can this provide geologists clues regarding Earth's past and history?

Where Does Sandstone Form?

Sandstone can form in any environment or circumstances that allow for deposition, compaction, and cementation. As previously mentioned, these processes can occur both underwater and on land. The different patterns, textures, framework grains, and matrix material can provide clues into the type of environment in which the sandstone formed during some time in Earth's geological past. Sandstone is abundant in areas that have been deserts for tens of thousands of years. Additionally, areas that may have been coastal regions facing oceans or the edges of lakes can produce sandstone. The patterns and textures in the sandstone can provide clues into the region's past. Patterns formed from compacted sand dunes on land appear different from the ripples created by flowing water or tidal and wave actions. Additionally, the composition of the sandstone provides information regarding the sandstone's source rock and source material. This information can help geologists understand the weather and climate of the past by explaining how wind or water carried the source material to its depositional environment.

Properties of Sandstone

The physical properties of sandstone can vary between different types of sandstone. As previously mentioned, sandstone is composed of the following:

A framework material which has to be clastic grains around 0.0625 and 2 millimeters in size;

A matrix material or fine-grained sediment that is introduced and surrounds the framework grains;

Properties of Sandstone

As we touched on in our description of the formation of sandstone, the properties of any given sandstone are quite variable. They can be formed under water or on land, holding clues in their coloring about their formation location. This is due to chemical differences that depend on oxygen being present in the rock-forming environment. Sand dunes can also be captured during rock formation, giving clues about the environment the sandstone formed in.

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Video Transcript

Sandstone Formation

Rocks are continually recycled, typically on timescales of millions of years, in what's known as the rock cycle. The three major types of rocks - igneous, metamorphic, and sedimentary - can each be turned into a new metamorphic rock when given enough heat and pressure. Each rock type can be turned into a new igneous rock if it is completely melted and then cooled again. Sedimentary rocks are made when other rocks are broken into fragments and those fragments are cemented together to form a new rock. One of the most common types of sedimentary rock is sandstone.

As the name implies, sandstone contains sand-sized grains of rock fragments and individual minerals broken down from other, older rocks. We all have a sense of how big sand grains typically are from our experience going to the beach or playing in a sand box. Geologists also know that sand-sized grains have a particular measurement, from about 1/16th of a millimeter to 2 millimeters.

We say source rocks, the original rocks that eventually make up the small grains of a sandstone, are weathered when they break down. The pieces coming off a source rock can then be eroded, or carried away from the source area. The longer the chunks of a source rock are carried by wind, water, or ice, the more likely they are to be broken down into very small fragments. Certain minerals found within rocks are also more likely to survive significantly long rock fragment travels. Because quartz is such a hardy mineral, unlikely to undergo chemical changes during erosion, it is the mineral found in the greatest amounts in many sands. On most beaches (and of course there are exceptions), you will find a lot of hard, almost clear-looking grains of sand, which are most likely quartz.

After a source rock is weathered and eroded, the resulting sand grains might fill a bowl-shaped basin on land or underwater. With the pressure from more sediments landing above and the movement of water through the grains, the sand becomes sandstone. Finer grains of rock and new mineral growth fill the spaces between the grains, cementing the new rock.

Properties of Sandstone

As we touched on in our description of the formation of sandstone, the properties of any given sandstone are quite variable. They can be formed under water or on land, holding clues in their coloring about their formation location. This is due to chemical differences that depend on oxygen being present in the rock-forming environment. Sand dunes can also be captured during rock formation, giving clues about the environment the sandstone formed in.

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Frequently Asked Questions

Is sandstone formed underwater?

Sandstone can form both underwater and on land. The texture and composition of the sandstone can provide clues to what kind of depositional environment existed in Earth's past that contributed to the sandstone's formation.

Why type of rock is sandstone?

Sandstone is a clastic sedimentary rock which means that sandstone is composed of clasts. Clasts are fragments of rock and sediments that originate from a source rock that underwent physical weathering in order to fragment. Sedimentary rocks are composed of sediments that undergo a process of compaction and cementation to bind into a rock.

How was the sandstone rock formed?

Sandstone forms from a framework sand grain material compacted by continued accumulating sediments and grains and then undergoes cementation. A matrix material, or finer-grained sediment, is introduced to the framework grains, most likely through saturation or flooding. This matrix material surrounds the framework, and then cementation occurs when additional minerals accumulate and grow between the framework grains before binding them into sandstone.

Why is sandstone a sedimentary rock?

Sandstone is sedimentary rock because it is composed of sediments that originated from a pre-existing rock before being eroded and deposited in a new location. In the depositional environment, the sediments undergo compaction and cementation.

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