Grain Size:
* Conglomerate: Contains rounded gravel-sized clasts (greater than 2 mm).
* Breccia: Contains angular gravel-sized clasts (greater than 2 mm).
* Sandstone: Contains sand-sized clasts (between 0.0625 and 2 mm).
* Siltstone: Contains silt-sized clasts (between 0.0039 and 0.0625 mm).
* Mudstone or Shale: Contains clay-sized clasts (less than 0.0039 mm).
Composition:
* Quartz sandstone: Predominantly composed of quartz grains.
* Arkose: Contains a significant amount of feldspar in addition to quartz.
* Greywacke: Contains a significant amount of rock fragments and dark minerals, often with a fine-grained matrix.
* Lithic sandstone: Composed primarily of rock fragments.
* Calcareous sandstone: Contains a significant amount of calcium carbonate (calcite).
Combination of Grain Size and Composition:
These two criteria can be combined to give more specific classifications, such as:
* Quartz conglomerate: A conglomerate composed mostly of quartz pebbles.
* Arkosic sandstone: A sandstone with a significant amount of feldspar grains.
* Calcareous siltstone: A siltstone containing a significant amount of calcium carbonate.
Other Factors:
In addition to grain size and composition, other factors can influence the classification of clastic sedimentary rocks, including:
* Sorting: The degree to which the clasts are of similar size.
* Rounding: The degree to which the clasts are rounded or angular.
* Matrix: The finer-grained material that fills the spaces between the clasts.
* Cement: The minerals that bind the clasts together.
By considering all of these factors, geologists can accurately classify clastic sedimentary rocks and understand the conditions under which they formed.
