CoachThe pores of a rock are the empty spaces between its grains and in its cracks. A rock with pores is porous. Its porosity is the share of its volume made of pores, written as a percentage.
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Example 17.5 (A cubic metre of sand)
One cubic metre of sand, full of water, holds litres of water in its pores. Of these, litres drain out by themselves; 30 litres stay stuck to the grains. One cubic metre of clay holds twice as much water, 500 litres, but only 20 litres drain out.