Limestone should not be used for grit. It will dissolve in the crop and gizzard, become soft and mushy, and will not grind up food. Limestone is famous for dissolving in acidic water in caverns and forming beautiful stalactites and stalagmites from the calcite solution as it drips from the cavern ceiling. In fact, the cavern itself was dissolved by the same water to form the big space in the limestone geological layer. Limestone was originally formed from living sea creatures and is of the exact same material as the oyster shell we give our layers. So, you may get the idea by now that limestone isn't a very hard rock and makes poor gravel and poor grit. Limestone grit can be used as an alternative to oyster shell for layers, though.
Granite grit is what you want for your chickens' gizzards. It will not dissolve in acidic water or inside a chicken's gizzard and will grind up food splendidly.
Granite grit is what you want for your chickens' gizzards. It will not dissolve in acidic water or inside a chicken's gizzard and will grind up food splendidly.