Geometrical characteristics of the seven crystal systems.
System 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 monoclinic
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).