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What are Sedimentary Rocks

Sedimentary rocks are shaped from deposits of pre-existing rocks or portions of once-living organism that accumulate on the Earth's surface. If sediment is buried deeply, it will become compacted and cemented, forming sedimentary rock. These rocks frequently have specific layering or bedding and create many of the picturesque views of the desolate tract southwest. Sedimentary rocks are categorized into three groups: Clastic, Biologic, and Chemical.

Key Terms

  • Cementation: The system via which clastic sediments turn out to be lithified or consolidated into hard, compact rocks, commonly via deposition or precipitation of minerals in the areas amongst the man or woman grains of the sediment.
  • Compaction: The technique of consolidating fine-grained sediments into rock.
  • Lithification: The conversion of free sediment into stable sedimentary rock. Several processes, which includes compaction of grains, filling of areas between grains with mineral cement, and crystallization act to solidify sediment.

Clastic Sedimentary Rock

Clastic sedimentary rocks are made up of portions (clasts) of pre-existing rocks loosened via weathering. These rocks have particles ranging in measurement from microscopic clay to massive boulders; their names are decided by using the clast or grain size. The smallest grains are referred to as clay, then silt, then sand. Grains large than two millimeters are referred to as pebbles. Some of the biggest examples of clastic sedimentary rock can be observed at: 

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  1. Arches National Park, Utah 
  2. Grand Canyon National Park, Arizona
Red Sandstone
A standard clastic sedimentary rocksandstone, seems crimson due to iron oxide.
Photo courtesy of Tina Kuhn

Biologic Sedimentary Rock

Biologic sedimentary rocks shape when dwelling organisms die, pile up, and are then compressed and cemented together. Types of biologic sedimentary rock consist of coal (accumulated plant fabric that is carbon-rich), or limestone and coquina (rocks made of marine organisms). Excellent examples of biologic sedimentary rock in country wide parks can be discovered at:

  1. Biscayne Bay National Park, Florida
  2. Guadalupe Mountains National Park, Texas
Coquina (biologic sedimentary rock) is a rock composed notably of marine fragments such as molluscs, brachiopods, foraminifera and invertebrates.
Photo courtesy of Tina Kuhn

Chemical Sedimentary Rock 

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Chemical sedimentary rocks shape with the aid of chemical precipitation that starts when water touring thru rock dissolves some of the minerals. These minerals are carried away from their supply and ultimately redeposited, or precipitated, when the water evaporates away. To view examples of chemical sedimentary rocks in the National Parks visit:

  1. Oregon Caves National Monument, Oregon
  2. Carlsbad Caverns National Park, New Mexico
  3. White Sands National Monument, 
Castile Evaporite
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Castile Evaporite (chemical sedimentary rock) of southeastern New Mexico and West Texas are interbedded layers of gypsum and calcite
Photo courtesy of Heather Walborn