Avian Calcium is a pure calcium supplement for all species of birds. The Avian Calcium uses only Precipitated Calcium Carbonate which is white in color and is essentially lead free. Impurities in other sources of calcium carbonate (e.g. Oyster Shell Calcium) cause the supplement to appear gray in color. The calcium carbonate particles in Avian Calcium have a unique shape, and an extremely high surface area per grams, resulting in increased calcium bio-availability. Calcium is essential for the formation and maintenance of strong bones, egg production, blood clotting, and other vital life functions. With Avian Calcium, you can take comfort in knowing that your birds are receiving a highly bio-available source of calcium carbonate that is free of harmful impurities.