I find i hard to believe it is the granite.. in the firs place, the granite is caught in the gizzard and acts like teeth to chew up the seeds and grain.. it passes out of the gizzard only after it is reduced to a very small size.. the gizzard acts like a rock polisher and the sharp edges would be removed by the time it passes on.. have you ever found large bits of rock in your chicken poo?? I don't think so..