Which property is common to both igneous and metamorphic rocks?

The property that solid, crystalline structures are common to both igneous and metamorphic rocks is grounded in their formations. Igneous rocks form when molten magma or lava cools and solidifies, resulting in a crystalline structure as the minerals within it crystallize. Similarly, metamorphic rocks originate from existing rocks—either igneous, sedimentary, or other metamorphic types—that have undergone significant changes due to heat, pressure, or chemically active fluids. These conditions promote recrystallization of the minerals, leading to the formation of a new solid, crystalline structure.

In contrast, sedimentation specifically pertains to the formation of sedimentary rocks, which involves the accumulation and compaction of sediments, and is not a process associated with igneous or metamorphic rocks. The presence of fossils is characteristic of sedimentary rocks, where organic materials can be trapped within layers of sediment, but is typically absent in igneous and metamorphic types. Therefore, the solid, crystalline structure is a defining aspect of both igneous and metamorphic rocks, highlighting their mineral composition and formation processes.