This is a very broad request. From what I can tell, the most frequent categories of impurities in unwashed sand are (a) salt and (b) silt and this depends on where the sand comes from.
Salty sand is not going to grow plants well at all. Silty sand might.
You can do an experiment. If you live near a natural source of sand (ocean beach or river bed), gather a bucket of it. Thoroughly wash half of it and then plant something easy to grow, like green beans, in each. You should have perhaps half a dozen seeds in each. Keep them together so that they get equivalent light and water.
My guess is that you will have your answer in just over a week.