Sorting describes the distribution of grain size
s, either in unconsolidated
deposits or in sedimentary rock
s. This should not be confused with crystallite
size, which refers to the individual size of a crystal in a solid. Crystallite is the building block of a grain. ''Very poorly sorted'' indicates that the sediment sizes are mixed (large variance
); whereas ''well sorted'' indicates that the sediment sizes are similar (low variance).
The terms describing sorting in sediments - very poorly sorted, poorly sorted, moderately sorted, well sorted, very well sorted - have technical definitions, and semi-quantitatively describe the amount of variance seen in particle sizes. See for details. In the field, sedimentologists
use graphical charts to accurately describe the sorting of a sediment using one of these words.
The degree of sorting may also indicate the energy, rate, and/or duration of deposition
, as well as the transport process (river
, debris flow
, etc.) responsible for laying down the sediment. Sorting of sediments can also be affected by reworking of the material after deposition, for instance, by winnowing
[Compton, R. R., 1962, ''Manual of field geology'', John Wiley & Sons, 378 p.]
Rocks derived from well sorted sediments are commonly both porous and permeable, while poorly sorted rocks have low porosity
and low permeability
, particularly when fine grained.