Helmenstine holds a Ph. She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter. Sand, silt, or clay sediment, called matrix , fills the spaces between the clasts and cements them together Conglomerate is relatively uncommon. Featured Video. Cite this Article Format. Helmenstine, Anne Marie, Ph. Conglomerate Rock: Geology, Composition, Uses. Get to Know 24 Types of Sedimentary Rock. Rock Provenance by Petrologic Methods.
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The matrix that binds the clasts together can be a mixture of sand, mud, and chemical cement. Common chemical cements are calcite or quartz. Conglomerate-Forming Environment: A beach where strong waves have deposited rounded, cobble-size rocks. If buried and lithified, these materials might be transformed into a conglomerate.
Conglomerate-Size Sediment Clasts: Pebble-size clasts of many compositions deposited together on a beach. Quartz, sandstone, and limestone clasts are all easily recognizable.
Largest clast is about two inches five centimeters across. Conglomerate forms where sediments of rounded clasts at least two millimeters in diameter accumulate. It takes a strong water current to transport and produce a rounded shape on particles this large. Wind transport is unlikely to produce a conglomerate. The environment of deposition might be along a swiftly flowing stream or a beach with strong waves.
These conditions might only be met during times of extreme flow or wave action. However, it is during these times that much of the Earth's sediments are picked up, moved, and deposited. To form a conglomerate, there must also be a source of large-size sediment particles somewhere up current. The rounded shape of the clasts reveals that they were tumbled for some distance by running water or moving waves. These conditions are found in streams, lakes, and oceans in many parts of the world.
Conglomerates often begin when a sediment consisting mainly of pebble- and cobble-size clasts is being deposited. The finer-size sand and clay, which fill the spaces between the larger clasts, is often deposited later on top of the large clasts and then sifts down between them to fill the interstitial spaces. After compaction, the precipitation of a chemical cement between the grains will bind the sediment into a rock. Breccia is a rock that is similar to conglomerate; however, the clasts in breccia are angular in shape rather than rounded like in conglomerate.
The shape of the clasts is the only physical difference between conglomerate and breccia. The specimen is about two inches five centimeters across. Conglomerate and breccia are similar rocks. They are both made of clasts over two millimeters in diameter. What's the difference between conglomerate and breccia? The difference is in the shape of the clasts. Conglomerate is made up mostly of subrounded to rounded clasts.
However, breccia is made up mostly of subangular to angular clasts. Sedimentary clasts can be angular or rounded. What determines the difference? They both start out at an outcrop a location where a rock unit is exposed at Earth's surface. This outcrop is known as the "source area" for the clasts. In the source area, chemical and physical weathering act upon the rock, causing it to break or disintegrate into smaller pieces.
These pieces are usually subangular to angular. Conglomerates can be further divided according to:. Class - conglomerate can be divided into two broad classes: Clast supported - where the clasts touch each other and the matrix fills the voids; and Matrix supported - where the clasts are not in contact and the matrix surrounds each clast;.
Sorting - a conglomerate comprising a mixture of clast sizes is poorly sorted, while one comprising mostly clasts of the same size is well sorted;.
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