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.
Click on image for full size
(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.

Last modified August 25, 2003 by Lisa Gardiner.

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