Which term refers to imperfections that extend along a line in the crystal lattice?

• A. Line Defect (Dislocation)
• B. Point Defect
• C. Resorption
• D. Growth Marks

Answer: (A)

Line defects are imperfections that extend along a line in the crystal lattice. They represent disruptions in the orderly arrangement of atoms that run through the crystal in one dimension. This is different from point defects, which are isolated missing or extra atoms at specific sites. The defects that run along a line are called line defects, with dislocations being the classic example. An edge dislocation occurs when an extra half-plane of atoms terminates within the crystal, creating a line of distortion, while a screw dislocation results from a shear that produces a helical ramp around a line. In gemology, dislocations can appear as linear features under magnification and influence the mechanical behavior of the crystal, as well as how light interacts with the lattice in some cases.