Difference Between Conglomerate and Breccia

Conglomerate vs Breccia
 

If you are not a student of geology, you might find talking about conglomerate and breccia very impossible, and you will not know the difference between them either. These are sedimentary rock types that are so similar that many question their classification into two different rock types. However, there are differences between conglomerate and breccia that will be highlighted in this article. The first fact one needs to understand when discussing these two rock types is that, all the difference between Conglomerate and Breccia stems from the way they are created. So, let us see how these rocks are created among other things.

It is easy to distinguish between breccias and conglomerates with naked eyes as grains are much large and easily seen with naked eyes. When the grain size is less than 2 mm, it becomes difficult to see them with naked eyes, and then the rock is simply categorized as sandstone.

What is Breccia?

Breccia is a name given to clastic sedimentary rocks that are formed by clinging together of a large number of angular fragments. Breccia is formed with the space between the fragments either filled by smaller fragments or mineral cement, which is responsible for holding the rock together.

Breccias get formed when host rocks break, and their debris are not transported to any far off place. This means that these rocks form when original rocks break and re-accumulate to make pieces that are angular in texture. Situations that often lead to the formation of breccias are landslides, impact craters, fault zones, explosions, and so on. Formation of breccias also takes place when meteors strike the earth and rocks are sent flying into the air. When these rocks fall back on earth, they join together to make breccias.

Cementing materials in breccias are normally calcite, quartz, gypsum, and clays. Even after formation, there are many pores or open spaces in breccias, which is why they are said to be a good rock to act as a reservoir of gases, ground water, and even petroleum. Breccias are angular in texture and are considered very good building material (ornamental). They are used for graves, making tiles, also for many other ornamental uses. Some breccias are considered precious and used in jewelry.

What is Conglomerate?

Conglomerate is also a type of clastic sedimentary rock that is formed by rounded fragments having joined together with the help of smaller such particles or with mineral cement that binds the minerals and fragments together.

If we take a closer look at the definitions of both types of rocks, we find that they are very similar to each other, containing similar ingredients, also both being sedimentary. Like breccias, conglomerates also form when pebbles cling together in a matrix and bind together by mineral cement. However, the major difference between breccias and conglomerates lies in roundness of grains. In conglomerates, the pebbles or grains are more rounded than in breccias, which indicate that their pieces have transported to a longer distance and have received impact by transporting material such as water.

Near the outcrop where breakage of rocks takes place, the pieces or fragments are angular, the breakage having resulted from mechanical weathering. However, the sharp edges of angular fragments get rounded when they are transported by water to large distances. These fragments are carried away from the outcrop and get cemented together after having been rounded because of the action of water.

Conglomerates, on the other hand, because of their irregular grain size, have less durability, and thus, used less often as a building material. They are beautiful, and thus, used in an ornamental fashion in buildings.

What is the difference between Conglomerate and Breccia?

• Shape:

• Breccias have angular fragments. In other words, Breccia has angular clasts.

• Fragments are much more rounded in conglomerates. In other words, Conglomerate has rounded clasts.

• This difference in grains is due to transportation of fragments, also because of the impact of transporting material (water).

• Forming Method:

• Breccias are formed as a result of violent situations where the rocks are broken and not transported well from their source. For example, landslides.

• Conglomerates are formed when the transporting energy such as water is high enough to move large rock particles.

• Strength:

• Breccias have greater strength than conglomerates.

• Uses:

• As a result of its strength, Berccia is more often used as building material.

• However, both breccias and conglomerates are used as ornamental material in buildings.

Images Courtesy:

1. Breccia by  Rygel, M.C. (CC BY-SA 3.0)
2. Conglomerate via Wikicommons (Public Domain)