system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes ivory different than normal bone and why is it so valuable?
gpt
Ivory is mammal tooth. It is primarily made of dentine.

Elephants have very large tusks (teeth) so were one of the only sources of very large pieces of ivory, since most teeth are quite small and even large tusks on many animals still are basically nothing when compared to the impressive tusks of the elephant. 

It is valuable because it is an excellent carving material.