In 3D lattice there are seven crystal systems.
1. Cubic 2. Orthorhombic 3. Tetragonal
4. Monoclinic 5. Hexagonal 6. Rhombohedral 7. Triclinic
NOW NOTE FIRST LETTER OF CRYSTAL SYSTEM
1.2.3. COT [ Kota ( hub of coaching industry)]
4.5.6.7. MHRT [ Maharashtra ]
In COT all crystallographic angles are equal and 90°
Triclinic is most unsymmetrical crystal system.