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         category includes ivory from both Indian and African elephants, as well as ivory from mammoths and mastodon. The tusks, or
         upper incisors, of these animals are used. They can have a cross section of up to 20cm (8"), and be up to 2.5m (almost
         3 yards) long. They are oval in cross section, and are made up of a hard, dense tissue called dentin, which is made up of
         70% inorganic material, and 30% collagen. 1. Elephant Ivory
Unlike human teeth, elephant tusks do not have an enamel coating. They do have a cementum layer,
         however; ivory dealers refer to this as the "bark" or the "rind". Occasionally this layer is retained
         on a piece of worked ivory. One-third to one-half of an elephant tusk is hollow.