Diagenesis: the physical, chemical or biological processes that turn sediment into sedimentary rock by modifying the mineralogy and/or texture.

Diagenesis occurs where the mineralogy of the rock becomes unstable as a result of changes in the conditions or chemistry. Instability usually occurs at grain contacts and in pore space between the grains. Changes in pressure and temperature cause new minerals to form or preexisting minerals to become modified as the sediment (or rock) adjusts to new equilibrium conditions.

There are 7 main diagenetic processes:

1. compaction
2. recrystallization
3. solution
4. cementation
5. authigenesis
6. replacement
7. bioturbation

The degree to which each of these processes contributes to the diagenesis of any given sediment is controlled by such factors as

• composition
• pressure (due to burial)
• temperature
• the composition and nature of the pore fluids
• grain size
• porosity, permeability
• the amount of fluid flow

Note that any sediment that has been deposited is subject to diagenesis, not just siliciclastics. The diagenesis of carbonate rocks has also been studied in great detail.

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