 However, in reality, most crystalline materials have a variety of crystallographic defects, places where the crystal's pattern is interrupted.The types and structures of these defects may have a profound effect on the properties of the materials.A few examples of crystallographic defects include vacancy defects (an empty space where an atom should fit), interstitial defects (an extra atom squeezed in where it does not fit), and dislocations (see figure at right).