What is grain size?
Grain size is a measure of the diameter of the particles in a sample. For this exercise the grain size values represent the average size of the particles in the deposit. Consequently, the deposit will contain some particles that are larger than the average and some that are smaller.
Grain size is typically measured by passing a sample through a series of sieves. Each sieve traps particles that are larger than the sieve screen size. The particles trapped on each sieve are then weighed and the amount of particles of a given size can be be determined.