petrology

Petrology is the branch of geology that studies rocks, their origin, composition, texture, and evolution. It seeks to understand how rocks form, transform, and interact within the Earth’s crust and mantle. Petrology integrates aspects of mineralogy, geochemistry, and tectonics to interpret the history recorded in rocks. The discipline is traditionally divided into igneous petrology, sedimentary petrology, and metamorphic petrology, each focusing on a principal mode of rock formation.

Igneous petrology examines rocks formed by crystallization from molten material, including intrusive plutonic rocks and extrusive volcanic rocks. Sedimentary petrology analyzes rocks formed by lithification of sediments through compaction and cementation, as well as rocks formed by chemical and biochemical processes. Metamorphic petrology studies rocks altered by pressure, temperature, and chemically active fluids, yielding foliated and non-foliated textures.

Texture and composition reveal history: grain size, shape, mineral assemblages, porphyritic textures, and metamorphic foliation. The rock cycle links formation through cooling, weathering, erosion, burial, metamorphism, and tectonic processes.

Methods include petrography with microscopic examination of thin sections, mineralogical analysis, X-ray diffraction, geochemical assays, isotopic dating, and electron microscopy. Petrology informs resource exploration, evaluating ore deposits, hydrocarbons, and geothermal energy; it also supports studies of crustal evolution, planetary geology, and environmental geology.