Geometrical characteristics of the seven crystal systems.

System	Axial lengths and angles	Unit cell geometry
cubic	a = b = c, a = b = g = 90°
tetragonal	a = b ­ c, a = b = g = 90°
orthorhombic	a ­ b ­ c, a = b = g = 90°
rhombohedral	a = b = c, a = b = g ≠ 90°
hexagonal	a = b ­ c, a = b = 90°, g = 120°
monoclinic	a ­ b ­ c, a = g = 90° b ≠ 90°
triclinic	a ≠ b ≠ c, a ≠ b ≠ g

Bravais Lattices

simple cubic		body-centered cubic		face-centered cubic

simple tetragonal		body-centered tetragonal

simple orthorhombic		body-centered orthorhombic		base-centered orthorhombic		face-centered orthorhombic

rhombohedral		hexagonal

simple monoclinic		base-centered monoclinic		triclinic

Some common directions in a cubic unit cell. The dot indicates the point where the vector exits the unit cell

Schematic representation of a close packed layer of equal sized spheres. The close packed rows (directions) are shown by the dashed lines.

Schematic represenation of two close packed layers arranged in A (dark grey) and B (light grey) positions. The alternative stacking of the B layer is shown in (a) and (b)

(a)

(b)

A schematic projection of the basal plane of the hcp unit cell on the close packed layers

Schematic represenation of the three close packed layers in a cubic close packed arrangement: A (dark grey), B (medium grey), and C (light grey).