Crystal symmetry
From Christoph's Personal Wiki
| Crystal Systems | |||
|---|---|---|---|
| System | Minimum symmetry | Dimensional requirements for unit cell | |
| Triclinic | none | none | |
| Monoclinic | Twofold axis (parallel to b) | a and c are both perpendicular to b (but not to each other) | |
| Orthorhombic | Three mutually perpendicular twofold axes | a, b, and c all perpendicular | |
| Tetragonal | Fourfold axis (parallel to c) | a, b, and c all perpendicular; a and b equal in length | |
| Rhombohedral (or Trigonal) | Threefold axis (parallel to c) | a, b perpendicular to c and at 120° to each other; a and b equal | |
| Hexagonal | Sixfold axis (parallel to c) | Same as trigonal | |
| Cubic | Threefold axes along cube diagonals | a, b, and c perpendicular and equal in length | |
