What is the Difference Between Sandstone and Shale

The main difference between sandstone and shale is that sandstone is a sedimentary rock mainly made of sand or quartz grains, while shale is a finely stratified sedimentary rock of silt and clay-size mineral particles.

Sedimentary rocks are a type of rocks that form via accumulation or deposition of sediment material. Sandstone and shale are two types of classic sedimentary rocks, usually common throughout the world.  

Key Areas Covered

1. What is Sandstone 
     – Definition, Features
2. What is Shale
     – Definition, Features
3. What are the Similarities Between Sandstone and Shale
     – Outline of Common Features
3. What is the Difference Between Sandstone and Shale
    – Comparison of Key Differences

Key Terms

Argillaceous Sandstone, Arkosic Sandstone, Sandstone, Shale, Quartzose Sandstone

What is Sandstone

Sandstone is a sedimentary rock mainly made of sand or quartz grains. Although it primarily consists of quartz, it may also contain a considerable amount of feldspar, as well as silt and clay. When sandstone contains more than 90% quartz, we call it quartzose sandstone. When it contains more than 25% feldspar, we call it arkosic sandstone. Moreover, when it contains a considerable amount of clay or silt, we call it argillaceous sandstone. The colour of sandstone varies depending on its composition. Most rocks usually have a light colour since they are made of light-coloured minerals. However, various shades of red are usually created by the presence of iron oxide.

Sandstone type typically has a rough and granular texture, just like sandpaper. Moreover, it is one of the most common types of sedimentary rocks in the world. You can easily find it in sedimentary basins all over the world.

What is Shale

Shale is a sedimentary rock formed from the compaction of silt and clay-size mineral particles we usually call “mud.” Therefore, we categorize shale as a type of mudstone. The main difference between shale and other mudstones is that shale is fissile and laminated. It is laminated because it’s made of many thin layers, and fissile because it can split into thin pieces along the laminations. Shale has different degrees of fissility. We can even describe shale as a thin layer of mudstone. Although shale mainly consists of mud and clay, there are also trace amounts of calcite and quartz.

Like sandstone, shale is also a very common type of sedimentary rock. It’s typically grey in colour, but this colour can change depending on the presence of other minerals. For instance, black shale is due to a high amount of carbonaceous matter. Likewise, red, green, and brown colours can occur due to compounds like ferric hydroxide, ferrous hydroxide, micaceous minerals, etc.

Similarities Between Sandstone and Shale

• Sandstone and shale are two types of classic sedimentary rocks.
• Moreover, both these types of rocks are very common throughout the world.

Difference Between Sandstone and Shale

Definition

Sandstone is a sedimentary rock mainly made of sand or quartz grains while shale is a finely stratified sedimentary rock of silt and clay-size mineral particles.

Composition

While sandstone is made of quartz, feldspar, as well as silt and clay, shale mainly consists of mud and clay, and trace amounts of calcite and quartz.

Structure

Moreover, sandstone is made of silt or clay that has been squeezed together to form a solid rock whereas shale is usually found in thin layers.

Properties

Sandstone has relatively coarse particles, which can be seen with the naked eye. It also has a rough and gritty texture like sandpaper. Shale, on the other hand, has very fine grains and often breaks into fragments.

Conclusion

Sandstone is a sedimentary rock mainly made of sand or quartz grains while shale is a finely stratified sedimentary rock of silt and clay-size mineral particles. Thus, this is the main difference between sandstone and shale.

Reference:

1. “Shale.” Geology, Available here.
2. “1.4 – Sedimentary Rocks.” Passel, Available here.
3. “Sandstone.” Minerals Education Coalition, 3 Apr. 2017, Available here.

Image Courtesy:

1. “Sandstone” By James St. John (CC BY 2.0) via Flickr
2. “Carbonaceous Shale” By Amcyrus2012 – Own work (CC BY 4.0) via Commons Wikimedia