Conglomerate Rock in Geology – Meaning, Uses, Facts, & Color

Conglomerate Rock in Geology – Meaning, Uses, Facts, & Color

Mar 27, 2023

In this knowledge-rich series of knowing rocks, we are going to know Conglomerate rocks, which are kind of sedimentary rocks and have some commercial values in different industries, particularly in construction businesses.

What Type of Rock Is Conglomerate

In geology, a conglomerate considers as a Clastic Rock. Here, clastic derived from the Clasts. The gravel-size pebbles, which are greater than 2 mm in diameter termed Clasts.

When the Matrix made of sand, silt, and clay particles and filled the gaps between clasts and also glues the clasts’ objects together, the formation of conglomerate takes place.

What Is Conglomerate Made Of?

The composition of conglomerate rocks have two major components:



In conglomerate rocks, the main framework grains are clasts, and those are always rounded or semi-rounded in shapes. [If clasts in a sedimentary rock have sharp corners, it is known as Breccia.] If a mixture of both kinds of clasts occurs in sedimentary rock, it refers to Breccia—Conglomerate Rock.

  • Rounded clasts may be mineral particles including Feldspar or Quartz.
  • The clasts may be fragments of Metamorphic or Igneous rocks.
  • The most common rocks forming clasts are
    • Quartzite
    • Sandstone
    • Limestone
    • Granite
    • Basalt
    • Gneiss


The following components are forming a matrix of the conglomerate rocks.

  • Sand
  • Silt
  • Clay/mud
  • Chemical cement

Cementing chemicals like NaCl and CaO bind the clasts together.

How Old Is Conglomerate Rock?

Jack Hills in Australia is a classic site where conglomerate rocks deposited in huge quantities. Upon geological tests, experts have revealed the fact that the oldest zircon crystals on the planet earth are embedded in the strata of these hills. The layers of Meta-conglomerate rocks have an age of more than four billion years, so it believes the oldest conglomerate rock on the planet.

Where Are Conglomerate Rocks Found?

We know the formation of conglomerate rocks takes place in the areas where an abundant supply of water from various water bodies is possible. Those water bodies may be

  • Lakes
  • Rivers
  • Sea Beaches with Strong Currents/Waves
  • Glaciers

Significant deposits of conglomerate rocks are found in the following areas of the world.


  • China
  • India
  • Kazakhstan
  • Mongolia
  • Russia
  • Uzbekistan


  • Namibia
  • Nigeria
  • South Africa


  • Austria
  • Denmark
  • Germany
  • Great Britain
  • Netherlands
  • Norway
  • Poland
  • Sweden
  • Switzerland
  • United Kingdom

North America:

  • Canada
  • USA

South America:

  • Brazil
  • New South Wales
  • New Zealand
Others: Greenland

The major deposits across the world noted by geologists are:

  • Many mountains and hills near Barcelona in Spain
  • The Crestone deposits in the San Luis Valley of Colorado
  • The abundance of rocks found in Northern Australia, Scotland, and Pennsylvania
  • Southern regions of the Indian Subcontinent

Conglomerate Rock Texture, Classification, and Types

Thanks to their clastic nature, conglomerate rocks have a clastic texture. The classification of conglomerate rocks depends on their clast’s compositions and compositions of the matrix content.

Let’s see details in a comprehensive format.

Conglomerate Classification According to Percentage of Cement



It is a matrix-supported type of conglomerate rock. When the percentage of the matrix in the rock is at least 15% and more, it terms as matrix supported.

This type of rocks is further classified into laminated (Cemented Clasts) & non-laminated. Tillites & Tilloids are respective examples of both.



On the contrary, these types of rocks have less than 15% matrix, and mass is dominated with clasts. Therefore, its terms as a clasts-supported conglomerate.

Conglomerate Classification Based on Resistance 

Petromict Conglomerate


Many natural stones have less withstanding capacities against weathering than others. When such clasts are present in conglomerate rocks those term as Petromict. Limestone, dolomite, shale, and similar stone clasts have low resistance power.

Oligomict Conglomerate


On the contrary, some clasts have high-resistance capacities and withstand against natural erosion and weathering impacts. For instance, quartz, chert, basalt, and others. When such clasts exist in the rock, those are term as Oligomict conglomerates.

Conglomerate Classification Based on Clasts and Cement Composition

Intraformational Conglomerates


When conglomerate rocks have the same kind of clasts and matrix, which originated from the same environment, those term as intraformational conglomerates. For example, a siliceous matrix with quartz and jasper clasts. Here, both rocks are of siliceous types and embedded into the siliceous matrix.

Extraformational Conglomerates


On the contrary, extra formational conglomerate rocks have different origin or types of clasts than the matrix. It is because clasts have transported from a kind of rock type area during matrix from another area. For instance, basalt clasts transported in a calcareous matrix area.

Conglomerate Classification Based on Variation in Parent Material

When the variation in parent material among themselves occurs, we can classify conglomerate based on those differences in the parent material. For example, similarities and differences between the clasts or matrix materials.

Monomictic Conglomerate


The same types of clasts found in the rock or parent material, it is monomictic conglomerates. Here, Mono means single and same.

Diamictic Conglomerate


When clasts are consisting of two types of parent rocks, it is a diamictic conglomerate. Here, Di- means two. For instance, quartz and Jasper clasts type found in the same conglomerate rock.

Polymictic Conglomerate


When numerous types of clasts exist in the same conglomerate rock, it is a polymictic conglomerate. Here, Poly- means many or multiple. For instance, quartz, basalt, limestone, and chert types of clasts are existing in the same conglomerate rock.


Conglomerate Classification Based on Size and Composition

Based on grain size and clasts size, we can classify conglomerate rocks in the following categories and types. The coarseness and fineness of rocks greatly depend on the size and compositions of the mineral grains/clasts embedded in the rocks.

Conglomerate Classification According to Grain Size

Very Coarse-grained Clasts size greater than 200 mm
Coarse-grained Clasts size between 20-200 mm
Medium-grained Clasts size between 6-20 mm
Fine-grained Clasts size between 2-6 mm

According to Clasts Size:

Boulder Conglomerate


Clasts size greater than 256 mm

Cobble Conglomerate


Clasts size in the range of 64-256 mm

Pebble Conglomerate


Clasts size between 4-64 mm

Granule Conglomerate


Clasts size between 2-4 mm


During the metamorphism process, the alignment of mineral clasts takes place in a single direction due to various factors including pressure and temperature.In due course, deformation of clasts and matrix also happens and leads to recrystallization matrix material takes place.


The resulting rocks have an inter-growth texture between the clasts, which used to found in low-metamorphosed stones. For example, when a sandstone converted to marble and clay in the rocks turned into slate.

Such metamorphosed conglomerate rocks are known as Meta-conglomerate.


Conglomerate Rock Colors

The colors of conglomerate rocks depend on the colors of clasts and matrix. If you find uniformity in the rock, the following colors are common.

  • Beige
  • Black
  • Brown
  • Buff
  • Light to Dark Grey
  • Orange
  • Rust
  • White
  • Yellow

How the Formation of Conglomerate Rocks Takes Place?

We know that conglomerate rocks always have rounded or semi-rounded clasts of a minimum of two millimeters in diameter. It means various rock fragments must be tumbled or transported in the streams or currents/waves of water, so those rock particles get a rounded shape.

It is possible in both freshwater and marine conditions. The geologies suggest the following different environments of depositions for conglomerate rocks in different parts of the planet.

Shallow Water Marine Environment:

At the coastal beach where the rocky edge is present, or river delta occurs, oceanic tidal waves are tumbling the gravels and pebbles and make well-rounded clasts with back-forth movements of water ripples. The deposition takes place with the pace of time and forms conglomerate rocks at the beach.

Similarly, in the lagoon, the formation of well-rounded, well-sorted, and fine-grained clasts takes place, and depositions along with sands, slits, and mud resulting in conglomerate rocks at the sea bed, coastal edges, and reef edges.

Deep Water Marine Environment:

At the delta region of a river mouth, clasts flow along with river flood currents and settle in the deep sea with each flood flow. It resulting into smaller but rounded and silt, clay, and sand rich conglomerate depositions in the deeper section of the sea.

Glacial Environment:

In high mountains, snow deposited during winter and forms glacial rivers or sheets of ice, which slowly flows toward the glacier mouth.

During the ice formation, the sediments that fall on the surface are being plucked by the solid ice and carrying along with during the journey of glacial mass.

When ice melts at the mouth, the “Glacial Till” is depositing on the ground and clasts are forming conglomerate rocks over time. Rocks are sorted poorly and coarse-grained in nature.

Alluvial Environment:

At the mountain front, streams are moving fast and empty in the plane lands. Force of water or water movement is slowing down, and water is dispersing in a broad area.

It eventually is resulting in depositions of mostly large and some small clasts. With the pace of time sedimentation process takes place and conglomerate rocks form.

Fluvial Environment:

In Latin, fluvial mean riverine environment. During floods in the river, a variety of clasts tumbled and transported further. Deposition of the moving mass takes place in the period in between the floods.
Transportation takes place for a long period, so it is resulting in the sorting and shredding of the size of clasts further, it makes clasts smaller more rounded in shape than at the upper stream of the river.

Therefore, the lacustrine environment yields graded bedding of conglomerate deposits.


What Are The Uses of Conglomerate Rock?

The use of conglomerate rock is somewhat limited in different industries due to its unreliable nature and different properties. However, the highest use is as aggregate raw material for roads and building industries. Let’s see some minor but significant uses of conglomerate rocks in a nutshell.

In Construction of Historic Buildings:

Near Barcelona, Spain, The Santa Maria de Montserrat Abbey was constructed using Conglomerate rocks obtained from Montserrat.

In Preparation of Construction of Aggregates:

Crushed conglomerates are excellent construction aggregate material for road and building construction industries. Conglomerates also used in cement manufacturing industry.

As Dimension Stones:

Conglomerates with smaller clasts size can cut easily in required shapes. If those are with good cementing material, the application as dimension stone for flooring and veneer on walls and roof tiles is possible.

As Decorative Material in interior and Exterior Application:

Clasts of conglomerate rocks have different parent material from a variety of natural stones. Therefore, those are coming in different colors, textures, and styles.

When cut in the right ways, these conglomerate rocks prove a decent decorative material for interior and exterior application in building construction industry.

As Architectural Stones for Curbing:

The entrance front always demands something different and unique to create great curbing appeal, and a conglomerate of different types provides enough options to go using the reliable and right materials.

As Antiquity Material:

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

In Other Commercial Applications:

In the past and present, conglomerate rocks are in use for cemetery markers, in the construction of aquifers, and tombstones.


Wrapping It Up

In the series of identifying various rocks and natural stones at World of Stones, USA, today we have explored some geological and industrial aspects of conglomerate rocks such as meaning, uses, facts, properties, and colors.

However, out of several suppliers of natural rocks, the World of Stones USA is an excellent choice for natural stones, particularly for exterior applications in the construction industry. If you have found our series interesting, keep the reading of blogs at World of Stones continue.



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