This winter, we had sand spread on the ice in our driveway. I've swept (and swept and SWEPT) it into a pile, and am wondering why I can't use it in my chicken run. It has a variety of coarseness, from pebbles to fine sand, and includes quite a bit of mica. Fellow New Englanders? Do you know if mica would be harmful to my chickens? Do you have a lot of it in your soil? It's shiny, so they might be attracted to it. Thanks!