I just learned a fascinating tidbit from Susan Tomes' Out of Silence: A Pianist's Yearbook: ivory from dug-up mammoth tusks can be crafted into piano keys. What's more, since mammoths are extinct, their ivory is legal, unlike that of their pachyderm cousins. Susan writes:
I'm astonished to think of slivers of deep-frozen tusk from thousands of years ago finding their way onto piano keyboards for the performance of Chopin and Liszt, and incidentally giving a fresh slant to that hackneyed phrase, 'a mammoth programme'.
Pianists and piano technicians: do any of you have any experience with this type of piano key material?