What characteristic distinguishes crystalline rocks from other rock types?

Crystalline rocks are primarily distinguished by their crystal structure. This characteristic arises from the way the minerals within the rock are arranged at the atomic or molecular level. In crystalline rocks, atoms are organized in a repeating, orderly pattern, forming well-defined crystals. This structured arrangement contributes to specific physical properties such as hardness, cleavage, and how the rock interacts with light.

In contrast, other rock types may exhibit different characteristics. For instance, sedimentary rocks may have a more irregular structure and can be characterized by layering due to the accumulation of sediments over time. Grain size refers to the size of the individual particles or crystals that make up the rock, which can vary widely among rock types, but it does not specifically define crystalline rocks. Porosity, another important feature, refers to the void spaces within a rock and is more relevant to the ability of the rock to hold fluids, rather than its crystalline nature. Hence, the distinct arrangement of minerals in a regular crystal structure is what truly sets crystalline rocks apart from other rock types.