Yep I've had exact thing happen to me too on a set of bone scaled I made :-( I was under the impression that it was ok for Ivory though, but I don't have any ivory scale at the moment...Mineral oil doesn't harm bone or ivory but I've seen personally where it absorbs into the scales and creates a look similar to oil on paper where it takes a slight translucence... And it cannot be removed sometimes even if you soak the scales in naphtha...
Users make your own decisions but just saying I've seen it... Ivory and bone should have a white color without being too dry
Edit here's a pic where someone did it on srp
View attachment 597521
See how the tip is translucent and darker?