Main Question or Discussion Point
My textbook states that all the 14 bravais lattices have one of the 7 types of parallelepiped (7 crystal systems) that can be used as an unit cell. However in case of 3D HCP textbooks don't talk about this parallelepiped, rather they consider a hexagonal prism as the unit cell. Why is it so? Also is this hexagonal prism a combination of rhombohedral and hexagonal crystal system?