iSCIENCE egg-emistry Eggs are laid by many creatures including reptiles, fish, birds –even a couple of rule-breaking 'monotreme' mammals. To survive in their own habitat, eggs can be soft-shelled, gel-covered, leathery, hard-shelled...or shell-less! Ostriches , c hickens, em u, quail. .. The hard-shelled y all la eggs but w ow what a diff er y in sizes! Whi ence ch one do yo u think is whi ch? egg-shell-ent birds... The shell of a bird's egg is made almost entirely of calcium carbonate (9497%). The rest is usually magnesium carbonate (1%), calcium phosphate (1%) and organic matter (1-4%). A strong protein matrix keeps the 'egg shape' firm. As it is semi-permeable, eggshell isn't entirely waterproof but should definitely prevent eggs drying out. Air and moisture pass through tiny pores and a thin 'bloom' coating helps keep out bacteria and dust. chromium eggs-tinction... Want your kit in 'team colours'? Painting your bedroom? The chemical often used to create these colours is '