RIO Grit Mixture For Digestion 520g (Pack Of 6) Mineral feed. Along with the main food, birds need to be constantly supplied with grit due to certain peculiarities of their digestive system. Organic and inorganic ingredients help to grind hard seeds in the muscular stomach of birds and serve as an additional source of calcium, phosphorus, sodium and other mineral substances. Coquina is the crushed marine shell and represents an important source of calcium, phosphorus, sodium and other minerals. Coquina dissolves in the acidic environment of the stomach; the obtained mineral salts can be easily absorbed in the bird's body. Coquina is especially necessary during the nesting period for building of strong eggshells as well as to maintain healthy bones and beak in chicks and adult birds.