This animation shows the process of formation of sandstone (hard rock) via the accumulation of grains of sand (sediments) at the bottoms of oceans.

After the sediments are deposited, they are covered by successive new layers and find themselves at greater depth under temperature and pressure conditions that are much greater than at the surface. The sediments undergo physical and chemical modifications (diagenesis) which transforms them into rock that is more or less hard and coherent.