April 28, 2015

Homework Help: Geography

Posted by pooleboy on Sunday, October 25, 2009 at 5:49pm.

I'm writing a paper about sedimentary rocks. My goal is 700 words but I'm stuck. can someone read this and let me know if I'm overlooking some important facts?
Sedimentary rocks are rocks that have accumulated at the surface of the Earth. These rocks, combined with hot lava, form a thin cover of material that make up the majority of the Earth’s crust (Answers Corp. 2009). They get their name from the term sediment which means to settle or small pieces. They get their start when weathered materials are exposed to different conditions. These conditions include rain, wind, heat, ice, waves, and even environmental chemicals.
Sedimentary rocks originate from sediments that accumulate as dust, sand, or mud. These sediments are deposited from water or air. They settle to the bottom of a body of water and, over time, these various sediments form layers. Sedimentary rocks can only be formed when sediments are deposited for a long enough length of time for them to be compacted in the strata. This compaction happens through the weight of the water and also the weight of the layers of sediment that are above it. The compactions results in the water being squeezed out of these layers. This causes the sediments to become cemented together by some of the different minerals that are in the water.
Sedimentary rocks are generally classified into three different categories. These categories are Clastic, Organic, and Chemical. Clastic sedimentary rocks are made up of separate and distinct pieces of materials that come from other minerals. Organic sedimentary rocks are true to their name. They are formed by organic materials from once living organisms. The mineral parts of animals, such as their bones and shells, are more likely to be preserved over time that their soft tissue is. These parts can become cemented together over time and this is what makes up the category of organic sedimentary rock. Plants can also be a part of the formation of sedimentary rocks. Plants that become compressed together over millions of years can form coal and coal is also a form of organic sedimentary rock. Just like the other two types of sedimentary rocks, chemical rocks also form at the Earth’s surface. They are typically found in horizontal layers but they are not formed by molten rock or clasts of sediment. Chemical sedimentary rocks are formed when mineral crystals from chemicals are dissolved in water. The water in areas such as oceans and lakes is often full of dissolved minerals and other elements. When the water is so full of elements, some are not able to remain dissolved. When this happens, they form solid mineral crystals or precipitate. Precipitation is the opposite of dissolving. As the water evaporates or when a chemical reaction occurs, the minerals precipitate. Evaporation takes only the water into the atmosphere leaving the remaining chemicals in a very concentrated state.

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