The Seven Crystal Systems
System Axial distances Axial angles Examples
Cubic a = b = c α = β; = γ = 90° NaCl
Tetragonal a = b ≠ c α = β; = γ = 90° SnO2, TiO2
Orthorhombic a ≠= b ≠ c α = β = γ = 90° KNO3
Monoclinic a ≠= b ≠= c α = β = 90°, γ ≠= 90° Monoclinic sulfur
Rhombohedral (or trigonal) a = b = c α = β = γ ≠= 90° As, Sb, NaNO3
Triclinic a ≠= b ≠= c α ≠= β ≠= γ ≠= 90° H3BO3
Hexagonal a = b ≠= c α = β = 90°, γ = 120° Graphite