Sedimentary rocks form when rocks and minerals are broken down into sediments. The term sedimentary is derived from the Latin word, sedimentum, which means settling. Sedimentary rocks can be classified based on how they are formed and their composition. The three main classes of sedimentary rocks are clastic, chemical, and organic.
Clastic sedimentary rocks are the most common type of sedimentary rocks. They are made up of minerals such as clay, sand, or gravel that has been broken down into smaller sizes due to a process called weathering. The sediments are also compacted and cemented together. Clastic sedimentary rocks are also classified by the size of the sediments in the rocks, coarse-grained, medium-grained, or fine-grained. Breccia is common type of coarse-grained clastic sedimentary rock. It has angular, large gravel sized particles. Sandstone is made from sand size grains or medium-grained sediments that have been cemented together. It also consists of pores which allow water, oil, and other fluids to move freely between individual grains of sand.
Chemical sedimentary rocks are formed when dissolved minerals are removed from a water solution. The formation of chemical sedimentary rocks involves the processes called precipitation and evaporation. Evaporation removes water and exposes the dissolved minerals. The high concentration of dissolved minerals is able to precipitate out of the water. The remaining minerals were left to build up on the bottom of the basin floor in places such as the Great Salt Lake in Utah. The accumulation of these minerals form chemical sedimentary rocks called evaporites. Rock salt and gypsum are examples of chemical sedimentary rocks.
Organic sedimentary rocks form from the accumulation of organic matter. Coal and limestone are examples of organic sedimentary rocks. Coal is made from the buried and compacted remains of plants that existed millions of years ago. Plants contain carbon. Limestone is made from the shells of organisms such as coral, clams, and oysters. These organisms use the mineral calcite found in lakes and oceans to make calcium carbonate. The calcium carbonate is used to build up their shells and skeletons. When the organisms die, the remains of their shells accumulate on the ocean floor. They form layers of a carbonate sediments and eventually limestone rocks. Tufa is a type of limestone rock formed in hot springs saturated with calcium carbonate.
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What type of igneous rocks is formed when magma cools and solidifies beneath the Earth’s surface?
Intrusive igneous rock
How are coarse-grained textures of most intrusive igneous rocks formed?
When magma cools slowly beneath the Earth’s surface.
How are the fine-grained textures of most extrusive igneous rocks formed?
The fine mineral grains form when lava cools very quickly.
What is the most common type of sedimentary rock?
clastic
What type of sedimentary rock is formed when dissolved minerals are removed from a water solution?
Chemical
This type of sedimentary rock is made from the remains of once living organisms.
Organic
What type of substance is made from non-living things?
Inorganic