Which of the following is an example of a crystalline structure?

A crystalline structure is defined by a highly ordered arrangement of atoms or molecules that form a repeating pattern in three-dimensional space. This regularity contributes to distinct properties, such as cleavage planes, which can be observed in these materials.

Diamond is an excellent example of a crystalline structure. Its atoms are arranged in a specific, repeating pattern that forms a rigid three-dimensional lattice known as a diamond cubic structure. This unique arrangement is responsible for diamond's notable hardness and brilliance. The strong covalent bonds between carbon atoms lead to its high stability and durability, factors that are characteristic of crystalline materials.

While quartz and graphite also have crystalline characteristics, their structures do not match the specific qualities of diamond in terms of regularity and bond strength. Gold, though it can form crystalline structures, is typically known for its metallic properties rather than the specific types of hardness and regularity associated with diamond.