Eggshell Powder Is an Effective Calcium Supplement for Plants and Pets Eggshells consist of calcium carbonate, along with small amounts of protein and other organic compounds. Calcium carbonate is the most common form of calcium in nature, making up seashells, coral reefs and limestone. Uses of Eggshell in our Gardens 1. As Fertilizers 2. Pest Control 3. Bird Food 4. Mulch 5. can be used also for pets nutrients and many other USES. Every packed weight 500 grams of Eggshell POWDER