Sedimentary Rocks Lesson

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From Sediments to Rocks

Sediments are broken bits of rock. They can be many different shapes, sizes, compositions and can be found in many different types of environments. In fact, all of these variations are unique to specific depositional environments.

There are three steps necessary to the formation of sedimentary rocks: Diagenesis, Recrystallization, and Lithification. The first, Diagenesis, was discussed in the Sedimentary Environments Lesson. Now we'll tackle the last two.

Step 2: Recrystallization

Recrystallization is the development of more stable minerals from less stable ones. Recall that minerals are stable under the conditions in which they form. Minerals at the top of Bowen's Reaction Series (olivine, augit, Ca-rich plagioclase) are less stable as they form at very high temperatures; minerals at the bottom of the Series (quartz, Na-rich plagioclase, and potassium feldspars) are the most stable as they form at lower temperatures. Example: Ca-rich plagioclase will alter to kaolinite.


Step 3: Lithification

Lithification is the process that transforms loose sediment into solid rock.

Burial -One layer of sediment piles on top of another
Compaction - Weight of overlying sediments reduces pore spaces, compacting the layers.
Cement - Mineral-rich fluids deposit minerals around grains / in pore spaces, “gluing” everything together.



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