The trigonal crystal system is closely related to the hexagonal system, and the two are often discussed together because they share the same basic arrangement of axes. Both use three horizontal axes separated by 120 degrees and a fourth axis set perpendicular to them. The difference lies in the symmetry of the internal structure. While the hexagonal system is defined by a six-fold rotational axis, the trigonal system is built around a three-fold axis. This means that a trigonal crystal looks the