I guess I need to clarify... I use the gray pigeon grit. While it does contain crushed granite, it also has other ingredients such as calcium chips (sometimes oyster shell depending on the manufacturer), charcoal, and a powdered vitamin/mineral mixture. Crushed granite alone would only help with seed grinding in the gizzard, but one would need to add other ingredients for calcium and other minerals as granite doesn't give them any of this. When I mentioned in the other post that I use the gray grit, I meant the gray pigeon grit. It's the same thing as red pigeon grit, minus the added iron. Otherwise they are both a mixture of crushed granite, calcium chips, usually charcoal, salt and a powdered vitamin/mineral mixture. The redstone you bought is a good grit as a trace mineral supplement (i'm pretty sure they make it out of clay). It's not a grit one would use as a grinding aid though. However it is a good additive during the breeding season as it does supply them with some additional calcium and whatnot.