A crystal is a solid with plane naturally occurring faces. An ideal crystal is defined to be a body in which the atoms are arranged in a lattice. A lattice is an infinite array of evenly spaced points which are all similarly situated. There are both internal and external symmetrical arrangements.
Crystals have different types of symmetry and different kinds of faces.
The three most common faces are triangles, squares, and rectangles. However, there are thirty-two possible classes of symmetry to which crystals can belong, this is including the class of no symmetry. Figure 10 shows the different types of fold symmetry. Another type of symmetry that may be unfamiliar to some is called the inversion symmetry. This type of symmetry is an operation that combines rotation and inversion.