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.
34 minerals
Hexagonal
Four axes, three equal in one plane, one perpendicular.
34 minerals
Trigonal
Rhombohedral
Three-fold rotational symmetry. Often grouped with Hexagonal.
2 minerals
Tetragonal
Three axes at right angles, one differs in length.
7 minerals
Orthorhombic
Three unequal axes, all at right angles.
25 minerals
Monoclinic
Three unequal axes, one pair not at right angles.
22 minerals
Triclinic
Lowest symmetry, three unequal axes, no right angles.
8 minerals
Amorphous
Non-crystalline
No regular crystal structure. Includes natural glasses and gels.
2 minerals