It is like really fine gravel for chickens....Mine were out on dirt during the day from 2weeks onwords, but to be on the safe side I found a big bag labeled "Chick Grit " at Tractor supply and bought that and added a little (a quarter cup to a gallon feeder) and mixed it into their feed-- I also mixed a cup into the soil in their dirt area-- I read somewhere not to offer just a tray of plain grit to chicks as they may just eat it straight and overdo it.... Worked for me and now that they are 5 and 8 weeks old respectively, and free range during the day, I dont offer it at all.....What exactly is grit? Mine are on a dirt floor in my feed room floor next to my barn, does the dirt floor give them grit, they also get a big clod of earth every morning with Huge Dandelions attached to it. Worms, bugs, greens and withing an hour, the dirt is all blended into the floor.