Material made from the dentine of different animals like elephant, hippopotamus, walrus or mammoth.
With the exception of mammoth, trading of ivory is only allowed with the appropriate CITES documents which you will receive upon reception of your instrument. We strongly recommend that you carry the neccessary documents at all times when you are travelling with an instrument that contains ivory (or other CITES materials).
Certain countries (such as the USA) prohibit the import of ivory completely. It is advisory to get proper information before you travel.
There is also so-called vegetable ivory made from the fruits of certain tropical trees.
More information about can be found in the book "Elfenbeinkunst" by P. W. Hartmann (german).