By river, ocean, or wind, rocks round the same way

Source: Science Daily

River rocks tend to be rounded, as do grains of dune sand and beach glass. Geophysicist Douglas Jerolmack of the University of Pennsylvania led a team in showing that all of these types of particles acquire a curved shape in a similar manner. The finding may help scientists understand how floodplains are built and predict when ash or dust clouds are likely to form.

https://www.sciencedaily.com/releases/2018/03/180328143320.htm