Which term is an imperfection or deviation from the ideal arrangement of atoms in relation to a single atom or point in the crystal lattice?

• A. Resorption
• B. Growth Marks
• C. Point Defect
• D. Singly Refractive (Isotropic)

Answer: (C)

A crystal’s atoms form an orderly, repeating array, and a point defect is a deviation that is localized around a single lattice site. This means one atom’s neighborhood isn’t arranged exactly as in the perfect lattice, creating an imperfection at that point. Common examples include a missing atom (vacancy), an extra atom sitting in an interstitial site, or a different atom substituting for the regular lattice atom (substitutional impurity). These defects are focused at or near one point, which is why they’re described as point defects. They help explain phenomena like color centers and how impurities affect a gemstone’s properties.

The other terms don’t fit because resorption isn’t a standard term for atomic lattice irregularities, growth marks are macroscopic growth-related features on the crystal surface, and singly refractive (isotropic) describes how light propagates through a material, not a localized atomic deviation.