The tip of a walrus tusk has an enamel coating which is worn away during the animal's youth. Fine longitudinal cracks, which appear as radial cracks in cross-section, originate in the cementum and penetrate the dentine. These cracks can be seen throughout the length of the tusk. Whole cross-sections of walrus tusks are generally oval with widely spaced indentations. The dentine is composed of two types: primary dentine and secondary dentine (often called osteodentine). Primary dentine has a classical ivory appearance. Secondary dentine looks marble or oatmeal-like.