Loose sediment, like that shown in (A) may someday become a rock like the one in (B) if compacted and cement fills the spaces between clasts.
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(A) courtesy of Bruce Molnia, Terra and (B) courtesy of Martin Miller, University of Oregon
Step 4: Lithification (From Pile of Sand to Solid Rock)
Sediment that has formed, been transported, and deposited, is not a sedimentary rock unless it is all bound together. The process of sediment becoming a rock is called lithification. It can take tens to hundreds of thousands of years.
The material that holds sedimentary particles together into a rock is called cement. Like the cement that holds bricks together in a wall, the cement in a sedimentary rock holds the bits of sediment together. However, the cement that holds a sedimentary rock together is a bit different because it is made of mineral crystals that form in-between the clasts and holds them together. Mineral crystals form from seawater or groundwater that travels through the empty spaces in-between clasts. The mineral precipitates out of water that contains the necessary chemical ingredients. Minerals like calcite, quartz, and sometimes hematite form the cement in sedimentary rocks.
Compaction also helps a pile of sediment to become a sedimentary rock. Compaction occurs when a layer of sediment is buried under other, younger layers of sediment, the clasts become squished closely together, filling in some of the porosity, the empty space between clasts.
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TES XXVI, 3 fall 2010
The Fall 2010 issue of The Earth Scientist
, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!
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