Breccia Rock

Definition –

Breccia (/ˈbrɛtʃiə/ or /ˈbrɛʃiə/) lithified sedimentary rock consisting of angular or subangular fragments larger than 2 millimeters (0.08 inch). It differs from a conglomerate, which consists of rounded clasts. The spaces between the large angular fragments are filled with a matrix of smaller particles and a mineral cement that binds the rock together.

The word has its origins in the Italian language, in which it means either “loose gravel” or “stone made by cemented gravel”. A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia, and hydrothermal breccia.

There are numerous modes of formation for breccia. Some constitute consolidated material accumulated on steep hill slopes or on the foot of cliffs. Cataclastic breccias are produced by using the fragmentation of rocks throughout faulting. Volcanic breccias (agglomerates) include blocks of lava in an ash matrix and are made of an explosive eruption. Hydrothermal breccias are shaped when hydrothermal fluid fractures a rock mass. Impact breccias are shaped whilst a meteor affects the Earth’s surface, fracturing rock on the website online of the impact. The cement that binds the clasts in a breccia is usually one in every of either calcite, silica or iron oxide. The matrix can consist entirely of the cementing cloth, but might also incorporate sand and/or silt-sized clasts cemented collectively a few of the coarser clasts.

Breccia can be found near landslides, fault zones and cryptolithicexplosion events. A breccia zone located near fault zones can varydrastically in size from inches to several yards. The other type is a gray rock known as lunar breccias. They are found at volcanic eruptions on Earth. On the moon, breccias were most likely formed by meteoroid impacts that melted the rocks together.

Formation of Breccia –

Breccia forms where broken, angular fragments of rock or mineral debris accumulate. One of the most common locations for breccia formation is at the base of an outcrop where mechanical weathering debris accumulates. Another is in stream deposits a short distance from the outcrop or on an alluvial fan.

There are three categories of breccia: sedimentary, pyroclastic or igneous, and cataclastic. The constituent fragments may be of one lithology such as a rock fractured in position, or of many lithologies suggesting accumulation from preexisting rocks. Void spaces between these clasts may be filled with a cementing material of carbonate, silica, or silt.

Breccia can be any color. The color of the matrix or cement along with the color of the angular rock fragments determine its color. Some breccias form from debris flow deposits. The angular particle shape reveals that they have not been transported very far (transport wears the sharp points and edges of angular particles into rounded shapes). After deposition, the fragments are bound together by a mineral cement or by a matrix of smaller particles that fills the spaces between the fragments.

Difference Between Breccia and Conglomerate –

Breccia and conglomerate are very similar rocks. They are both clastic sedimentary rocks composed of particles larger than two millimeters in diameter. The difference is in the shape of the large particles. In breccia the large particles are angular in shape, but in conglomerate the particles are rounded.

The particle shape reveals a difference in how far the particles were transported. Near the outcrop where the fragments were produced by mechanical weathering, the shape is angular. However, during transport by water away from the outcrop, the sharp points and edges of those angular fragments are abraded and rounded. The rounded particles would form a conglomerate.

Types of Breccia –

There are many different names of breccias. It given names to common used when referring to a rock or rock debris made up of angular fragments. Although it is mainly used for rocks of sedimentary origin, it can be used for other types of rocks.

Collapse Breccia: Crushed rock that reason from a cavern or magma chamber collapse.

Fault Breccia or Tectonic Breccia: Crushed rock found in the contact area between two fault blocks and produced by movement of the fault.

Flow Breccia: A lava texture produced when the crust of a lava flow is broken and jumbled during movement.

Fold Breccia: formed by the folding and breakage of thin, brittle rock layers which are interlayered with incompetent, ductile layers.

Igneous Breccia or Volcanic Breccia: A term used for a rock composed of angular fragments of igneous rocks. “Flow breccia” and “pyroclastic breccia” could be called “igneous breccia.”

Impact Breccia: A deposit of angular rock debris produced by the impact of an asteroid or other cosmic body. See an article about “impactites.”

Monomict Breccia: whose clasts are composed of a single rock type, possibly all from a single rock unit.

Polymict Breccia: A breccia whose clasts are composed of many different rock types.

Pyroclastic Breccia: A term used for a deposit of igneous rock debris that was ejected by a volcanic blast or pyroclastic flow.

Chemical Composition of Breccia –

Breccia has many compositions. Its composition is mainly determined by the rock and mineral material that the angular fragments were produced from. The climate of the source area can also influence composition. Most breccias are a mix of rock fragments and mineral grains.

The type of rock that the fragments were produced from is often used as an adjective when referring to the rock. Some examples: sandstone breccia, limestone breccia, granite breccia, chert breccia, basalt breccia, and others. Often a breccia will contain many types of angular rock fragments. These are known as polymict breccias or polymictic breccias.

Uses of Breccia –

For thousands of years, the striking visual appearance of breccias has made them a popular sculptural and architectural material. Breccia was used for column bases in the Minoan palace of Knossos on Crete in about 1800 BC. Breccia was used on a limited scale by the ancient Egyptians; one of the best-known examples is the statue of the goddess Tawaret in the British Museum. It was regarded by the Romans as an especially precious stone and was often used in high-profile public buildings. Many types of marble are brecciated, such as Breccia Oniciata or Breche Nouvelle.

The word “breccias” is used as a trade name for a group of dimension stone products with a broken, angular pattern. Names such as “Breccia Oniciata,” “Breccia Pernice,” and “Breccia Damascata” are cut and polished limestones and marbles that reveal a broken, angular pattern. These breccias are used as architectural stones for interior building veneers, tiles, window sills, and other decorative applications. These are proprietary names applied to the rock from specific quarries.

 

Information Sources:

  1. geologyscience.com
  2. britannica.com
  3. geology.com
  4. wikipedia