Grains of sand are really very tiny particles of rock. It takes time and certain kinds of weather to turn rock into sand. Rain, frost, and wind can do the job. At beaches, the tide hitting against the rocks forms sand. Salt water, too, forms sand by dissolving minerals in the rocks.
Since rocks are made up of minerals and since sand comes from rocks, you would expect to find lots of minerals in sand. There are, in fact, large quantities of quartz and also some lime, gypsum, feldspar, and even iron ore in sand.
the answer is: it comes from rocks -_-