What is a key feature of crystalline structures?

A key feature of crystalline structures is the presence of regular, repeating geometric patterns. In crystalline solids, atoms are arranged in a highly ordered and repeating manner, which extends throughout the material in three dimensions. This ordered arrangement gives rise to specific properties such as distinct melting points and the ability to exhibit anisotropy, where the material can have different properties in different directions due to its structural configuration.

The regular geometric patterns in crystalline structures are essential for the stability and uniformity of the material. For example, common examples of crystalline materials include table salt and diamonds, where the predictable arrangement of atoms leads to specific characteristics like cleavage planes and symmetric shapes.

In contrast, the other options describe characteristics more typical of amorphous solids or non-crystalline materials, which lack this orderly arrangement. Such materials have no long-range order and exhibit irregular patterns that do not repeat consistently. This difference is critical when examining the behavior and properties of various materials in engineering applications.