We call these crystalline building block unit cells. A unit cell represents the miimun repeating pattern that describes the three-dimensional array of atoms in a crystalline structure, or crystal lattice, of a solid. Think of unit cells as microscopic analogues of the repeating patterns you may have seen in fabrics, wrapping paper, or even a checkerboard, as illustrated in Figure 11.8. Look carefully at the image in Figure 11.8a to confirm that the outlined portion represents the minimum repeating pattern. A unit cell serves a similar function: it is the three dimensional pattern of atoms, ions, or molecules that is repeated throughout a crystalline solid. The six-sided cell in Figure 11.6 is called a hexagonal unit cell.