Natural processes, like rain and snow, help minerals become rocks.
Rocks are classified as sedimentary -- one of the three major rock types -- if they are composed of compacted sediments. Sediments are loose particles of rock, called lithics, or minerals that originate from the weathering of rock or from precipitation out of solution.
Transportation
After sediments are formed, they are usually transported some distance before they can settle and become sedimentary rock. Gravity, wind, water and ice are all possible transportation agents. During transportation, larger fragments weather down to smaller fragments. This weathering results in rounding of the sediment grains as they come in contact with each other and other abrasive materials. Another result of transportation is sorting, which is a grading of sediments based on their size. Smaller fragments are often transported longer distances than large fragments and sorting is a display of this.
Deposition
Deposition is the settling of sediments that occurs when a transportation agent no longer has the necessary energy to transport the sediments. Environments of deposition are highly variable and include locations such as river channels, desert valleys and the ocean floor. In sedimentology the environment of deposition gleaned from the study of a sedimentary rock is a key factor in determining ancient geologic environments of a region and how they may have changed over time.
Preservation
For sediments to finally become a sedimentary rock, it is important that they be preserved between deposition and lithification. For preservation to occur the sediments must not erode and undergo transportation after deposition. Sediments deposited on land are easily eroded and have a low chance of preservation, while sediments deposited underwater have less chance of erosion and a higher chance of preservation.
Lithification
Lithification is the term used to describe any process that turns sediments into sedimentary rock. This can be accomplished through some combination of compaction and cementation. Compaction is the packing together of grains, reducing the pore space between them, and can be caused by burial beneath more sediment. Cementation is when naturally formed cement is precipitated around the sediment, holding the grains together in a consolidated form. This can occur from groundwater moving through the sediments and leaving elements behind in the sediment as it flows. Some sedimentary rocks can also form by mineral crystallization. This is when elements of the grains and cement react to form new minerals that grow in an interlocking arrangement and hold sediment grains together.
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