INTRODUCTION

      There is a lot of sand in a desert and I want to know how the sand got there. We start with the the form of the Earth the main crustal  [the crust of the Earth] elements [which are O, SI and Al], which have to be mixed with the first crustal rocks. The main crustal rock is a granite . 

The reaction

          There is a reaction that controls the nature of quartz in the granite. The size control works in the granite. When the granite weathers, sand particles appear.

putting it together

      Once a place becomes arid [dry] there is no water to hold the finer particles of clay and organic matter down. So the wind takes over and blows those particles.

forming sand

    The finer particles can be blown into rivers places that were less arid at the time and be washed right down the less arid places. Which could form a fraction of a desert.

Not too fast....

       Sand has a lot of small particles of larger rock that has been broken down, but that doesn't happen fast enough for that to be the only reason there is sand in the desert .

conclusion 

     In conclusion, these are the main reasons how sand gets in a desert.