Upon completion of this module, you should be able to describe the triclinic and cubic lattice and explain the difference between primitives, body-centered, and face-centered cubic lattices. Crystals are solid substances with a lattice structure. A crystal lattice consists of a series of repeating subunits called unit cells. The shape of a three- dimensional unit cell is defined by an array of points known as lattice points. Three vectors, labeled a, b, and c determine the spatial arrangement of lattice points in three dimensions. The three angles formed by these vectors are termed alpha, beta, and gamma.