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.
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 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.
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.
We can also mention a third way lithification is accomplished and that is through recrystallization. This is the process by which unstable minerals recrystallize into stable minerals causing grains to bind together. As the name implies, there are already crystals formed, but these crystals may be unstable in a given chemical environment.
These unstable crystals reform or recrystallize, and as they do, they grow and bind together forming rock. This is a chemical process, and we tend to see this process at work in the formation of certain types of limestone and other chemical sedimentary rocks because their minerals can be less stable and therefore may change with shifts in the chemical environment.
- Lithification is the process by which sediments combine to form sedimentary rocks.
- Compaction is a consolidation of sediments due to the intense pressing weight of overlying deposits. With compaction, sediment grains get squished together, reducing the size of the original pore space that divided them.
- Cementation is the process by which dissolved minerals crystallize and glue sediment grains together.
With cementation, we see that water with dissolved ions seeps into remaining pore spaces. The ions get deposited in the spaces and then crystallize, forming new minerals that grow and glue the unconsolidated grains together into rock.
- Recrystallization is the process by which unstable minerals recrystallize into stable minerals causing grains to bind together. In certain chemical environments, unstable crystals reform or recrystallize causing them to grow and bind together as rock.
Upon completing this lesson, you should be able to:
- Define lithification
- Explain how each of the three lithification processes occur