rockformation

Rock formation refers to the processes by which rocks originate and are modified into the three major rock types: igneous, sedimentary, and metamorphic. These processes operate over timescales from thousands to millions of years and depend on temperature, pressure, fluid chemistry, and tectonic context. The study of rock formation underpins geology, landscape evolution, and natural-resource distribution.

Igneous rocks form by cooling and solidification of molten material. Intrusive rocks crystallize underground to make coarse textures such as granite; extrusive rocks erupt at the surface and cool quickly, producing fine-grained rocks like basalt or rhyolite. Composition ranges from felsic to ultramafic.

Sedimentary rocks form from the accumulation and lithification of sediment derived from preexisting rocks or organisms. They are classified as clastic, chemical, or biochemical. Features such as bedding, fossils, and ripple marks record depositional environments and history.

Metamorphic rocks arise when existing rocks are altered by heat, pressure, and fluids without melting. This changes mineralogy and texture, creating foliated rocks such as schist or nonfoliated rocks such as marble. Metamorphism occurs during tectonic burial, mountain building, or contact with magma.

Surface weathering and erosion sculpt rock formations and, together with tectonics, drive the rock cycle, the ongoing transformation among the three rock types over geological time.