Complex sentence: It's crystal system is Tetragonal and it's crystal class is 4/m, which is also called the tetragonal-dipyramidal class because it only has a vertical four-fold rotation axis that is perpendicular to the symmetry plane.
Split into simpler sentences: It's crystal system is Tetragonal and it's crystal class is 4/m. The 4/m class is also called the tetragonal-dipyramidal class because it only has a vertical four-fold rotation axis that is perpendicular to the symmetry plane.