It does look like ivory of some type, but not made out of one tusk and split. The dark color is only on one scale, looks like dye or maybe burned? The checkering was done by a amateur probably after the handle was put on the knife. It is hard to follow the lines and keep them straight on a curve. If it is ivory, it would be pretty heavy, about the only way to tell for sure is to have the scales removed and I don't think that is possible without damage. As you probably know, walrus ivory has some "cracked ice" looking grain on the interior if observed by the end grain.