Rounding of grains are normally studied on grain-sizes between 16 and 64 mm (pebble). The figure below shows pebble with different degree of rounding, which reflects whether they have been smoothed by contact with other grains or not.  For example, pebble in a glacier, with limited contact during transport, are typical angular.  On beaches or in rivers grains are constantly polished by direct contact into typical well rounded grains. Degree of rounding of a sample of pebble is classified  by sorting a certain amount of pebbles, e.g. 100 grains, into the different categories shown in the figure.Such data contributes to classification of type of sediments.

Click on the figures to enlarge it.

In which category do the particles in the photo belong?