My guess is that it is made from Mammoth tooth material. Its a beauty!
Mammoth tooth fossils (yes it is a fossil and not ivory) may not be as old as other "elephant" types like the Mastodon, so the degree of fossilization can vary... they tend to be very brittle (even almost glass like), so I would protect it from impact and you will want to be very careful about how tight you keep the hilt on the keris (snug, but not real tight... or crack)....
http://www.150.si.edu/150trav/discover/d123a.htm
http://www.tellmewhereonearth.com/im...0TOOTH%202.jpg
http://www.acnatsci.org/museum/jeffe...mammuthus.html