Poultry Grit Mix Flint Grit & Limestone Grits With Oyster & Cockle Shell Added Charcoal for Palatability Feathers & Beaky Chicken Grit is a mixture of flint grit & limestone grit, oyster shell, cockle shell and charcoal. Flint grit acts like teeth in the crop to help chickens grind up their food. Limestone grit, oyster & cockle shell have a high mineral content, including the all-important calcium, for good shells on their eggs. Charcoal enhances the palatability of food & aids digestion