Cubic System and Crystal Forms

Common minerals : Galena, Garnet, Fluorite, Magnetite

• Crystallographic axis : a₁ = a₂ = a₃ , a₁ ^ a₂ ^ a₃ = 90⁰
• Characteristic Symmetry elements :
  • Axis of symmetry : 4 of 3 fold

Classes of the system

1. Normal class/ Galena type
   • Plane of Symmetry : (9) 3-axial, 6-diagonal
   • Axis of symmetry : (13) 3 of 4 fold & 4 of 3 fold & 6 of 2 fold
   • Centre of symmetry : present
2. Pyritohedral class/ Pyrite type [Gyroidal]
   • Plane of Symmetry : 3-axial
   • Axis of symmetry : (7) 3 of 2 fold & 4 of 3 fold
   • Centre of symmetry : present
3. Tetrahedral class/ Terahedrite type
   • Plane of Symmetry : 6-diagonal
   • Axis of symmetry : (7) 3 of 2 fold & 4 of 3 fold
   • Centre of symmetry : present
4. Plagiohedral class/ Cuprite type
   • Plane of Symmetry : No
   • Axis of symmetry : (13) 3 of 4 fold & 4 of 3 fold & 6 of 2 fold
   • Centre of symmetry : present
5. Tetartohedral class/ Ullamanite type
   • Plane of Symmetry : No
   • Axis of symmetry : (7) 3 of 2 fold & 4 of 3 fold
   • Centre of symmetry : No

Unit forms of Normal class :

Form	No. of faces	Miller Indices
Cube	6	100
Rhombdodecahedron	12	110
Dodecahedron	8	111
Tetrahexahedron	24	hko (210)
Trisoctahedron	24	hhl (221)
Trapezohedron	24	hll (211)
Hexoctahedron	48	hkl (123)