3D-rotations lie at the core multigrain crystallography, texture analysis, and many other topics in materials science.
Typically, one describes the orientation of a crystal lattice by a set of rotations relative to an external reference frame. Unfortunately, there are many ways to do so! Do you want to rely on Euler angle triplets, in the what convention, axis–angle pairs, quaternions, Rodrigues–Frank vectors, rotation matrices, homochoric representations? What are the sign conventions? How do you convert from one to the other?
If you want to dig into this topic, you may look at