Breccia is a group name for a set of clastic sedimentary rocks made of large angular fragments. The angular fragments are usually over two millimeters, filled with smaller particles and mineral cement that binds the rock together.
An interesting thing about breccia is that it can be of various colors. Its color depends on the matrix, cement, or the color of angular fragments.
Megabreccia: It is a type of breccia that is made of very large rock fragments. The deposits can be several kilometers across and form due to landslides, impact events, or caldera collapse.
Breccia is a typical sedimentary rock formed when broken and angular rock fragments, mineral dust, and debris accumulate. The outcrop base is the most common spot for breccia formation, where mechanical weather debris gathers. You may find its deposits in streams near outcrops or alluvial fans.
Breccia can also form due to debris flow accumulation. Once deposited, the fragments are bound by mineral bonds or smaller particles matrix. The angular particle shape identifies the rocks formed due to debris flow accumulation. These rocks have pointed angular particles because transport converts the angular particles into rounded edges.
Breccia’s composition can vary from one specimen to another. Its composition is usually determined by the mineral fragments and the rock from which it was created. The climate of the region where the rock is formed also impacts its composition.
The type of rock often defines breccia it is produced from. For example, you will find breccia referred to as limestone breccia, sandstone breccia, chert breccia, granite, breccia, and basalt breccia. Some breccias contain various types of angular fragments.
Types of Breccia
Breccia are classified based on their formation mechanism
Sedimentary: It is formed as a result of a sedimentary process. Some common examples include scree deposits at the base of a cliff, submarine debris flow, rock collapse into a sinkhole, or cave development.
Fault: Fault breccia forms two fault blocks that pass each other. Subsequent cementation of the broken fragments occurs when the mineral matter is introduced.
Igneous: Igneous breccia is of two types: volcanic and intrusive. Volcanic breccia is formed by the eruption of lava and rocks trapped within the eruptive column. Intrusive breccia is formed in shallow sub-volcanic intrusions like granite and kimberlite pipes.
Impact: Impact breccia form from an impact event like an asteroid or comet hitting the earth. These rocks are usually found at impact craters.
Hydrothermal: These breccias generally form at shallow crustal levels (less than 1 kilometer) with temperatures between 150 and 350°C. The rocks form when seismic or volcanic activity opens a void along a fault line deep underground. The void draws in hot water, forcing the pressure in the cavity to drop. The rocks at the side of the fault destabilize and implode inwards; the broken rocks are caught up in a mixture of hot water, rocks, and steam. Rock fragments collide, edges are rounded, and rocks are formed.
Monomict: Breccia that forms from a single rock type. Ideally, all rock from a single type.
Polymict: Breccia that forms from different types of rocks.
Breccis vs. Conglomerate
Breccia is often confused with the conglomerate. The two rocks are clastic sedimentary rocks made of particles bigger than 2 millimeters. The main difference is in the shape of these particles; breccia has angular particles, and conglomerate has rounded particles.
The particle shape also reveals an interesting fact; breccia forms near the outcrop and the particles don’t travel much distance. The conglomerate has rounded particles, and these rocks are formed when the debris flow travels a lot of distance due to water away from the outcrop.
Where is Breccia Found?
Breccia is a common rock and is found in many countries. Its reserves are located near landslides, fault zones, and volcanic events.
Breccia is found in different colors. Its biggest use is to make sculptures, architectural elements, and ornaments. It has been used throughout our history to make sculptures and statues. The most famous include the Minoan palace of Knossos (Europe’s oldest city) and the statue of goddess Tawaret made by ancient Egyptians. Romans regarded breccia as a precious stone to be used in high-profile buildings and palaces.
Due to its attractive appearance, breccia is often used as an architectural stone, tile, window sills, and in other decorative applications.
Breccia is not used in construction projects because its hardness and cementation are highly variable, and it doesn’t offer the strength required for such tasks.