In my own less than educated opinion, I'd also say this is legit ivory.
Also, another relevant imitation ivory is "French ivory." This is an early cellulose/plastic material that does have layers that kind of, but not really, resemble the Schreger lines you'd find on actual ivory.
I'm including two images from an old auction, and a link to my own small gunong with a French ivory hilt, previously discussed on the Ethnographic side of the fence.
http://www.vikingsword.com/vb/showthread.php?t=24831
Have fun,
Leif