Knowra Eggshell Eggshell An eggshell is the hard, porous outer covering of a bird’s egg, made mainly of calcium carbonate. Its pores permit gas exchange while its structure protects the developing embryo.
Calcium carbonate : A chemical compound, CaCO₃, found in limestone, shells, and many biological structures. It forms most of the mineral layer that gives eggshells their hardness.
Calcite : A crystalline form of calcium carbonate and the most stable polymorph at Earth’s surface. Most of the mineral in typical bird eggshells is calcite.
Eggshell waste : Discarded eggshells produced by households and food industries. Large food-processing streams make shell disposal and reuse practical concerns.
Reptile egg : An egg laid by a reptile, commonly enclosed by a leathery or rigid shell depending on the species. Many reptile eggs lack the thick, highly calcified shell typical of bird eggs.
Eggshell porosity : The capacity of an eggshell to let gases and water vapor pass through microscopic pores. Pore number and size shape the exchange of oxygen, carbon dioxide, and water vapor.
Mammillary layer : The inner mineralized layer of a bird eggshell, where crystal units begin growing from the shell membranes. Its crystal foundations anchor the calcified shell to the underlying membranes.
Eggshell-derived calcium : Calcium-rich material recovered from eggshells for use in products such as supplements and biomaterials. The shell’s calcium carbonate can be processed into useful calcium-containing materials.
Amphibian egg : An egg laid by an amphibian, usually surrounded by a gelatinous coating rather than a rigid mineral shell. Its soft outer covering contrasts with the bird eggshell’s calcified barrier.
Avian egg gas exchange : The diffusion of respiratory gases between a developing bird embryo and its surroundings through the egg’s shell and membranes. Embryos depend on shell pores to obtain oxygen and release carbon dioxide.
Palisade layer : The thick middle layer of a bird eggshell, made of tightly packed columns of calcite crystals. This layer supplies much of the shell’s thickness and mechanical strength.
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