Rhombic primitive lattice

Figure 2.3 The relationship between the rectangular (oc) lattice (a) and (b) the equivalent rhombic primitive (rp) designation of the same lattice...

In two dimensions the unit cell is a parallelogram whose size and shape are defined by two lattice vectors a and b). There are five primitive lattices, lattices in which the lattice points are located only at the corners of the unit cell square, hexagonal, rectangular, rhombic and oblique. In three dimensions the unit cell is a parallelepiped whose size and shape are defined by three lattice vectors (a, b and c), and there are seven primitive lattices cubic, tetragonal, hexagonal, rhombohedral, orthorhombic, monoclinic, and triclinic. Placing an additional lattice point at the center of a cubic unit cell leads to a body-centered cubic lattice, while placing an additional point at the center of each face of the unit cell leads to a face-centered cubic lattice. 

A Figure 12.4 The five two-dimensional lattices. The primitive unit cell for each lattice is shaded in blue. For the rhombic lattice the centered rectanguiar unit cell is shaded in green. Unlike the primitive rhombic unit cell, the centered cell has two lattice points per unit cell. 

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