Deall, I have personally used silica sand for sand blasting.....and with very great care. I had to wear an industrial dust mask and a hood. It can be very nasty stuff for the lungs and you'll find that info easily online. I doubt particle size matters since it's all very fine. I believe I once saw some of kind of condition called "silicosis" but you'd need to check yourself. For me, it's best and broadest uses are industrial, should stay that way and finding any possible alternative for using with potted or other landscape plants is preferable. Isn't it used in Quickcrete? I hope you can find something like coarse pumice or sharp sand or grit of some kind, mabe Dry Stall. Good luck, Pamela