Shell is the outer skeleton of mollusks. It is created by the epithelium of a skin fold, which usually consists of three layers: outer (conchiolin), middle (calciferous) and inner (so called mother of pearl). The two last layers are built mostly from calcium carbonate. Shells has always been of interest for people due to the variety of shapes, colors and effective patterns. Undoubtedly it is one of the most astonishing natural creations.
