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Lithification of Sediments: Definition & Processes

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  • 0:06 Lithification
  • 0:58 Three Ways…
  • 1:26 Compaction
  • 2:37 Cementation
  • 3:34 Recrystallization
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Lithification is the process that turns loose, unconsolidated sediment into solid sedimentary rock. Learn about the three ways lithification is accomplished, including compaction, cementation and recrystallization, in this lesson.

Lithification

Sedimentary rocks are created when little pieces of sediment, such as pebbles, sand and clay, join together. Okay, that seems simple enough, but how do these little pieces of sediment stick to each other to form a solid rock?

If you think about it, you could go down to the beach and pick up a handful of sand and try to squeeze the sand grains together really hard, but once you open your hand, the sand will run through your fingers. You could try wetting the sand with water. This would hold the sand together for a short time, but once that water evaporated, the sand grains would once again separate.

So, there must be some trick to get sediments to combine and form solid rock. In this lesson, we will learn about something called lithification, which is the process by which sediments combine to form sedimentary rocks.

Three Ways Lithification Occurs

The term lithification is derived from the Greek language. And it might help you to remember the meaning of this term if you recall that the prefix 'lithos' is Greek for 'rock.' So, we are really looking at the making of rock when we study lithification. There are two main ways that lithification occurs: compaction and cementation. We will also touch on a third way that is important to some sediments, called recrystallization.

Compaction

Compaction is the consolidation of sediments due to the intense pressing weight of overlying deposits. Compaction happens when sediments get buried. This literally squishes the sediment grains together, compressing them into a mass. With sufficient pressure and the passage of time, the grains get rearranged and more organized, much like winning a game of Tetris where the majority of the falling tiles fit snuggly together. As the sediments consolidate, the original pore space that divided them is reduced and any water that was in those spaces is squeezed out.

We see compaction happen with all sizes of sediment grains, but generally the larger sediments do not compact as successfully because their large grains are harder to fit together. However, finer grains of sediment, such as clay, tend to lithify better because these fine grains attract each other. For example, if you place a bowl full of grapes, which represents pebble-sized sediment grains, next to a bowl of flour, which represents clay-sized sediment grains, it's easy to see that compaction works better for smaller grained sediments.

Cementation

Another way lithification of sediments occurs is through cementation. Cementation is the process by which dissolved minerals crystallize and glue sediment grains together. This is an easy term to remember if you think of it like you would a bag of cement. A construction worker will take a bag of powdery cement and mix it with water to bind particles together.

With cementation, we have minerals that grow and bind sediment together. The act of cementation is really what forms our sedimentary rocks. Compaction certainly helps the process along by bringing the individual grains close together, but even after compaction, there are spaces remaining between the grains. These spaces can be filled with water that contain dissolved ions. The ions get deposited and then crystallize, forming new minerals between the sediment grains. These minerals grow and glue the unconsolidated grains together into rock.

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