Also, when you do begin to give it to them I suggest sprinkling it over their food like salt and not putting it in a separate container. I did that and one of my chicks thought the grit was it's actual food and would sit there and eat that all day instead of her chick starter. Putting it in a...
I just checked and I use the same brand. My chicks haven't had a problem with it so I'm sure it's fine. Mine wasn't dusty when I opened the bag so maybe yours was just shaken around a bit more or crushed finer.
I searched google, and the best answer I can give you is that if it contains silica it should say so on the package. If it's grit specifically made for chickens, it shouldn't contain silica because the maker should know how poisonous it is for the chickens.
If your using coarse sand or...
Chicks don't really need grit unless they are eating treats and such. If they are just on the regular chick feed they don't need it. Once you begin feeding them treats (meal worms, grass, oats, etc) is when they need the grit.