Sand dunes become sedimentary rock through cementation. This
happens in several stages. First, after the sand dune forms, it is
usually buried below the Earth’s surface as newer sand dunes cover it.
Second, during and after the dune is buried, water within the ground
begins to move through it. The water flows in the spaces or pores
between individual sand grains. This water often contains dissolved
silica (SiO2) or calcium (Ca) and carbonate (CaCO3).
If the chemical conditions are right, the third stage, cementation, will
occur. Quartz or calcite crystals will precipitate in the spaces between
the sand grains. They will grow until the spaces are filled up,
effectively cementing the sand together.
Sand Mountain in Fallon, Nevada
Sand dunes in Oregon, USA