  As an expansion of complex numbers, the quaternions show close relations to
numerous physically fundamental concepts. In spite of that, the didactic
potential provided by quaternion interrelationships in formulating physical
laws are hardly regarded in the current physics curriculum. In particular, many
approaches emerge that are useful in conveying the unity of seemingly distinct
theories in a didactically convincing manner. This will be exemplified with the
help of special relativity. The diverse examples of spatial and space-time
rotations are merged into a didactic whole by introducing quaternion
transformations and comparing them to the representation using rotation
matrices common in physics books.
