for fracking, what they want is a perfectly uniform sized quartz grain thats rounded. You find this sand where multiple processes occur, notably glacial geology. You want uniform grains because frackings goal is to open, then support an porous structure when you can then pull the fluids/gas out without clogging.

It's not really hard to test for this property, but the cost efficiency is notable when you find a massive amount of it in one place. It still may be washed to remove further silt/clay, but they absolutely know the product works and they generally know the geology in other places don't tend to produce the same material.

There's a fair amount of materials size thats mostly "we found this geologic material and this is some magic shit" rather than some wholly manufactured human endevour.