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°
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