Detritic or clastic sedimentary rocks

Detritic or clastic sedimentary rocks represent 80-90% of all the sedimentary rocks. They can be separated into two main classes  

The strength of cementation is often an important characteristic in engineering terms. Well-cemented quartz sandstones can be very strong mechanically, whereas friable uncemented sandstones are relatively weak rocks. Siltstones, mudstones and shales are usually weak rocks because of the dominance of platey clay minerals that provide little frictional resistance. Moreover, conglomerates and sandstones exhibit relatively high volumes of void fraction (i.e., porosity) and are economically important as aquifers for water supply and reservoir rocks for gas and petroleum. 

Class Paricle Unconsolidated Consolidated (i.e., cemented) rock type  

6 Medium sands Medium often thickly bedded, depositional structures 

S sandstone such as cross-bedding common. Arkose sand- 

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