I'm not saying there is silica in it. A lot of people on here recommend it because it is clean but all I can get around here has silica in it. I actually had my local pool store call their distributor to find out and sure enough there was silica in it. I've heard the easiest way to tell is if there is silica in it then you will see glass like sand pebbles.
As far as the white stuff... hopefully someone with a little more knowledge will chime in!