Conglomerate – Rock: Geology, Composition, Classification and Uses

An introduction to Geology

Geology is rightly referred to as the study or science of the earth. Many people associate Geology with the study of rocks only. However, Geology is much deeper and more profound than that. It is not only about studying and analyzing rocks. It studies our planet, its mineral, resources and formations deeply.

We also interact with Geology in our daily lives. Our mobile phones, notebooks, household items, make-up, etc are all made of minerals that have been studied in Geology. In addition to this, Geology also deals with natural disasters like rockfalls, landslides, earthquakes, quick clay, and radon and their analysis and prediction. Not only this, but it also works to understand climate change and therefore is extremely relevant in this day and age. These studies help predict the future state of our planet and thereby work to identify contaminants and protect the environment for the future. Geology also plays a significant role in studying rocks and minerals. Studying rocks and minerals are crucial because it gives us a glimpse of what the Earth may have been like in the past. These rocks can also be used for several practical purposes.

In this article, we will study about a unique rock called conglomerate. We will study its composition, texture, formation, types, and uses.

Geology Conglomerate

The conglomerate is a sedimentary rock made up of rounded pebbles and sand that is usually held together (connected) by silica, calcite, or iron oxide. Conglomerate sedimentary rock is a stone similar to sandstone but rock particles are angular gravel or rounded rather than sand. 

Conglomerate refers to coarse-grained rock that is formed in riverbeds. The pebbles and sand can be made up of many minerals, but it is generally quartz-based minerals.

The hardness of the conglomerate sedimentary rock is variable, and it often resembles concrete. It is generally found in thick, crudely, and stratified layers. Conglomerates are generally used in the construction industries as decorative stones.

Conglomerate Composition

There can be a variety of conglomerate compositions. As a clastic sedimentary rock, it can include clasts of any rock material or weathering product that is washed downstream or down current. The rounded clasts of conglomerate can be mineral particles such as quartz, or they can be sedimentary, metamorphic, or igneous rock particles. The matrix that joins that large clast together can be a mixture of sand, mud, and chemical cement.

Conglomerate Rock Classification

The classification of conglomerate rock is based on the following factors:

  • Amount and type of the matrix present in the rock

  • Composition of the gravel-sized clasts they contain

  • Size range of gravel size clasts present 

The classification method of conglomerate rock depends on the detail and type of the research being carried out.

Conglomerate Characteristics and Properties

The main conglomerate characteristic is the presence of readily visible, rounded clasts bound within a matrix. The geology conglomerate is a sedimentary rock type that looks like concrete. It comprises large, rounded pebbles ( clasts) joined by a matrix made up of calcite, iron oxide, or silica.

The conglomerate property depends on its composition.  It can be found in any other colour and may be either hard or soft.

The conglomerate can be used as a fill material for roads and constructions. Hard rock may be cut and polished to make dimension stone.

Conglomerate Uses 

Conglomerate uses are very rare because of their non clean breakage and fine particles are reliable. It can only be used as a crush where low-performance material is required. Conglomerates can be crushed to make a fine aggregate that can be used for roads and buildings in construction industries. Conglomerates are also used in the cement manufacturing industry.

Most of the conglomerates are colourful and have attractive looks, but they are only rarely used as ornamental stone for interior use.

Conglomerate with smaller clasts size can be easily cut in the required shapes. If the conglomerate found is with good cementing material, its application as dimension stone for flooring and veneer on walls and roof tiles is possible.

Conglomerates are providing excellent material for monuments, artifacts, and sculpture formation, and in the creation of small figurines.

Conglomerate Rock Formation

Conglomerate rocks are formed by larger pieces of sediments, such as sand and pebbles. The pieces of sediments in conglomerate rocks can be very big ( like boulders) or very small (like peas). Most conglomerate rock formation occurs in shallow water. Conglomerate rock is formed by pressure and joined together with dissolved minerals. Conglomerate rocks are used in the construction industries and as decorating stones, such as for buildings.

Conglomerate Rock Texture and Types

The conglomerate sedimentary rock contains at least 30% rounded to sub angular clasts larger than 2mm (0.079) in diameters such as granules, cobblers, pebbles, and boulders. However, conglomerates are rarely composed entirely of gravel size clasts.  Generally, the space between gravel sizes is filled by a mixture composed of different amounts of silt, sand, and clay known as matrix. 

If the individual gravel clasts in a conglomerate are set apart from each other by a plethora of matrices such that they are not in contact with each other and float within the matrix, it is considered a paraconglomerate. Paraconglomerate is also often not stratified and can comprise more matrices than gravel clasts. If the gravel clasts of a conglomerate come in contact with each other, then it is called an orthoconglomerate.


These are conglomerates that have been sorted poorly. They are matrix rich conglomerates These are believed to have been formed as debris flow on alluvial fans. They carry the largest amount of accumulations ever known in the field of Geology.


When conglomerate rocks undergo metamorphic alteration, they turn into metaconglomerates. They might have deformed clasts as compared to usual conglomerates. They break through grains as the cement in them has recrystallized. These are most famously found in the Jack Hills of Western Australia. It is these rocks that are believed to have produced zircons from 4.4 billion years ago.

Puddingstone Conglomerate

These are simply conglomerates that have a sharp contrast of colour within their clasts. This is not a scientific name but is simply used to identify such rocks. They are found in several parts of the world including the UK, France, Canada, India, USA, etc.

Did You Know?

  • Conglomerate rock is believed to be the oldest rock on the Planet as the layers of meta conglomerate have an age of more than 4 billion years.

  • Conglomerate rock is a sedimentary rock consisting of individual clasts with a finer-grained matrix that has been cemented together.

  • Conglomerate rock differs from breccia by its rounded clast. (Breccia is a rock very similar to conglomerates. However, they are different due to the presence of having subangular to angular clasts).

  • Interestingly, in 2012 conglomerate was discovered on Mars by  NASA's Mars rover Curiosity. Since these are found in places where water flowed once, the presence of these rocks on Mars is by far one of the most important pieces of evidence of the presence of water on Mars.

FAQs (Frequently Asked Questions)

1. What are the Different Colours of Conglomerate Rocks?

The colour of conglomerate rocks depends primarily on the colours of clasts and matrix. If you find uniformity, the following conglomerate rock colours are commonly found:

  • Beige

  • Black

  • Brown

  • Buff

  • Light to Dark Grey colour

  • Orange

  • Rust

  • White 

  • Yellow

As can be seen, conglomerate rocks can be found in a variety of colours and have no one in particular. The colour is largely dependant on their composition. 

2. Where are Conglomerate Rocks Found?

As we know, conglomerate rock formation occurs in areas where an adequate supply of water from different water bodies is possible. These water bodies include lakes, rivers, glaciers, and sea beaches with strong current waves. Significant deposits of conglomerate rocks are found in the areas such as Asia, Africa, Europe, North America, South America, Australia, and others. Since these rocks are found around water bodies as rock-fall and debris flow deposits along cliffs, they are very commonly found due to the abundance of such areas.

3. Which Type of Rock is Considered a Conglomerate?

In Geology, a conglomerate is considered a clastic rock. Here, the term clastic is derived from clasts. The gravel-sized pebbles, which are more than 2 mm in diameter are termed clasts.

When the matrix is made of sand, silt, and clay particles and fills the gaps between the clasts and also joins the clast object together, then the conglomerate formation takes place.  So these are essentially sedimentary types of rocks that are composed of a good amount of clasts that give them their unique colours.

4. What are some key characteristics of conglomerate rocks?

Conglomerate rocks have some unique properties associated with them. Some of these are:

  • Rounded clasts are present in a matrix. (Clasts are gravel-sized pebbles)

  • The clasts are readily visible.

  • The rocks are present in varying colours.

  • They have variable hardness. Thye may be present in the form of a conglomerate with a soft matrix and even in the form of a hard conglomerate.

The properties of conglomerate rocks largely depend on their composition. These rocks are found in places in places that had flowing water once. They may be also found in places that contained glaciers at some point in time.

5. Why must we study geology?

Geology may seem like an unimportant science to many. However, it is not simply the study of rocks. It largely investigates the subterranean world of our planet. It is important also because it explores natural resources, analyzes and predicts natural disasters, works to understand the climate of our planet, etc. there are many other important areas related to sustainability that come under the science of geology.  At Vedantu we understand the significance of every subject. you can visit our website and read about Structural Geology and other Earth sciences in detail.