Nonsedimentary

Nonsedimentary is a geological term used to describe rocks not formed primarily by the accumulation and lithification of sediment. In common usage it covers igneous and metamorphic rocks, which originate through entirely different processes from sedimentary rocks.

Igneous rocks form by cooling and solidification of molten material. They can crystallize below the surface as intrusive (plutonic) rocks such as granite and diorite, or erupt at the surface as extrusive (volcanic) rocks such as basalt, rhyolite, and obsidian. Their textures range from coarse-grained to glassy, reflecting cooling rates.

Metamorphic rocks arise when pre-existing rocks are subjected to elevated heat, pressure, and/or chemically active fluids, causing mineralogical and textural changes without melting. They are commonly foliated (slate, schist, gneiss) or non-foliated (marble, quartzite, hornfels). Metamorphism can occur on regional scales or locally during intrusion of hot magma.

Nonsedimentary rocks contrast with sedimentary rocks, which originate through deposition, compaction, and cementation of sediments. The boundaries between categories are not always sharp, as some rocks can undergo partial melting or be formed in environments influenced by both sedimentary and igneous/metamorphic processes over time.

Economically and geologically important nonsedimentary rocks include granite, basalt, marble, and slate. They are widespread in continental crust and contribute to construction, industry, and landscape formation.