A tusk is a tooth of the upper jaw of the mammoth (or elephant). A major blood vessel branching off while running to the tip can easily be seen. The caves on right hand side are assumed to stabilize this life long weapon of a mammoth.
This tusk has been stone age ivory and consists mostly of calcium phosphate and calcium carbonate.
As there is no restriction to trading of mammoth ivory there is an increasing amount of siberian stone age ivory emerging to the market.