My bedding in the coop and run is sand, so when they do get treats and scratch, they also consume some of the sand with it. They also cruise around in the garden and lawn area when they free range so they eat dirt along with the weeds and grass. I did research commercial grit and pretty much figured out that it is basically sand. The type of sand in my coop is coarse, like construction sand.
Construction sand is ideal, especially if you can find it by the truckload. I know there used to be some concern about tge bagged stuff at Home Depot/Lowe's/Menard's because it wasn't washed or something. If I had a run, I'd definitely be doing sand likecwe did before we moved.
I have a container of grit, but I'm pretty sure they're eating the driveway.