Seven types of crystal system

Crystals along with suitable examples are listed in the table.

System	Axial distances	Axial angles	Examples
Cubic	a = b = c	α = β = γ = 90°	NaCl,KCl, Diamond, Cu, Ag
Tetragonal	a = b ≠ c	α = β = γ = 90°	White tin,SnO2
Orthorhombic	a ≠ b ≠ c	α = β = γ = 90°	Rhombic — Sulphur, KNO3, K2 SO4, BaSO4, PbCO3
Monoclinic	a ≠ b ≠ c	α = γ = 90°, β ≠ 90°	Monoclinic sulphur, Na2 SO4 .10H2O
Hexagonal	a = b ≠ c	α = β = 90°, γ = 120°	Graphite, ZnO, CdS
Rhombohedral	a = b = c	α = β = γ ≠ 90°	Calcite, quartz, NaNO3
Triclinic	a ≠ b ≠ c	α ≠ β ≠ γ ≠ 90°	CuSO4.5H4O, K2Cr2O7

In the above description, it was assumed that the particles are present only at the corners of the unit cells. Such type of unit cells in which particles are present only in the corners are called Simple Unit Cells.

But it has been observed that the particles may also be present at some other special positions within the unit cell. Such unit cells are called non-primitive unit cells.