The majority of the pieces I've seen resembling the size, shape and colors of the pieces you've illustraded are animal bone. Usually very thin (not as thick as a stick of chewing gum). They could very well be ivory, but without a visual examination and not knowing what to look for, one can easilly mistake bone (or even Celluloid-type plastics) for ivory.

Also, please feel free to drop the Mr.

JB