Here's why:
* Quartz: Quartz is incredibly resistant to weathering and erosion. This means it survives the breakdown of parent rocks and gets transported long distances, becoming a dominant component of sediment.
* Feldspar: While less resistant than quartz, feldspars are still relatively common and can be found in varying degrees of alteration.
Other common minerals in clastic sedimentary rocks include:
* Micas: These are sheet silicates that are relatively resistant to weathering, but less so than quartz.
* Clay minerals: These are formed by the breakdown of other minerals, especially feldspars, and are often abundant in finer-grained sediments.
* Carbonates: While carbonates are more common in chemical sedimentary rocks, they can also be present in clastic rocks, particularly in areas with a significant carbonate source.
The specific mineral composition of a clastic sedimentary rock will vary depending on:
* The source rock: The original rock from which the sediment originated will determine the starting mineral composition.
* Weathering conditions: The type of weathering will influence which minerals are most resistant and therefore most likely to be preserved.
* Transportation distance: Long transportation distances tend to concentrate the most resistant minerals like quartz.
* Depositional environment: The environment where the sediment is deposited can affect mineral composition, for example, coastal environments might have more carbonates.
Overall, quartz and feldspar are the most common minerals in clastic sedimentary rocks due to their resistance to weathering and their abundance in the Earth's crust.
