Question: how does sand rock form?

Jon Copley answered on 13 Jun 2010:

First, you need to make sand, which forms from rocks as they get bashed about and ground together by the movement of water in riverbeds or on rocky beaches. Sand can also form from rock fragments created by “freeze-thaw” weathering, where water trickles into cracks in rock formations and freezes during cold nights. As water expands when it freezes, this can ping bits off rock faces.

Once you’ve got your sand grains, they get carried in rivers or water currents (or by air across deserts) until eventually they sink from whatever flow is carrying them to form sand beds. As these sand beds grow, their weight starts to squeeze the sand at the bottom of the bed.

Eventually this squeezing pushes the sand grains together enough to form sandstone, with a little help from some minerals that also act as a cement. Where water is flowing through the spaces between the sand grains, minerals dissolved in the water can precipitate out of solution (a bit like the limescale you can get in a kettle or a washing machine) to bind the sand grains together and form the sandstone.