[gus_massa]

Wool is mostly keratin, also hooves and nails.

And feathers, turtle shell, but they are made or another type of keratin.

To be honest, each the keratin of each animal is slightly different, with small changes of the composition, something like plastic that can be made softer or harder tweaking the compostition.

Anyway, I guess it's not about the exact composition, but the "magic" part of the rhino horn.