When's the last time you saw a chicken tooth?
Grit takes the place of what teeth do...it grinds and crushes the food in the gizzards. Your birds should always have some on hand. Birds will self-regulate their grit intake, so no worries about overdoing it. But if they need some and can't get to any, they may end up with digestive problems. Keep a bit out for you egg-laying friends at all times.
100% crushed washed rose quartz
Store in a dry place.