Crystal Systems
Minerals are classified into seven crystal systems based on the geometry of their unit cell — the smallest repeating unit of their structure. The system reflects the symmetry of the crystal lattice and determines the external shape of well-formed crystals.
Cubic
Isometric
Highest symmetry — three equal axes at right angles.
28 minerals
Hexagonal
Four axes — three equal in one plane, one perpendicular.
28 minerals
Tetragonal
Three axes at right angles — one differs in length.
6 minerals
Orthorhombic
Three unequal axes, all at right angles.
18 minerals
Monoclinic
Three unequal axes — one pair not at right angles.
18 minerals
Triclinic
Lowest symmetry — three unequal axes, no right angles.
4 minerals
Amorphous
Non-crystalline
No regular crystal structure. Includes natural glasses and gels.
1 mineral