2015-3-6 · corners. Crushed sands contain between 1% and 25% of platy mica particles. Natural sands exhibit a wider range of shapes; typically: roundness R=0.3-to-0.9 and sphericity S=0.5-to-0.9. Margaret river sand has very smooth texture while Ponte Vedra and Jekyll Island sands contain a significant percentage of platy crushed shells.