Others exist but are rarely found on knives. Appreciation of or preference for a particular type of ivory is, again, a matter of personal choice. Elephant ivory is generally white or off-white with a fine grain and is great for carving and scrimshaw. Walrus ivory generally runs from tannish brown to black in color. I tend to choose the blacks, reds, greens and blues for my projects.
Mammoth ivory has a similar type of coloring .
Other than color a big difference between the types of ivory is how porous they are. Mammoth is, in my opinion, not as porous as walrus or elephant. In general these materials can range from smooth to a crysted stag-like appearance after finishing. I have finished walrus and mammoth from stone-like all the way through to a rough look depending on the total picture of the knife. As a buyer you have to expect cracks in all of these materials.