petrologi

Petrology is the branch of geology that studies rocks and the processes that form, transform, and classify them. It aims to understand the origin, composition, texture, and distribution of rocks on Earth and other planetary bodies, linking mineralogy, geochemistry, and field geology.

The main subfields are igneous petrology, which investigates rocks formed by the cooling of molten material; sedimentary petrology, which analyzes rocks formed by lithification of sediments; and metamorphic petrology, which examines rocks altered by heat, pressure, and chemically active fluids. Economic petrology focuses on mineral resources, while experimental and planetary petrology extend the study to high-pressure experiments and extraterrestrial rocks.

Petrologists use a range of methods, including petrographic microscopy of thin sections, field mapping, geochemical analyses (XRF, ICP-MS), mineralogical techniques (X-ray diffraction), isotopic dating, and electron microscopy. They interpret rock textures, mineral assemblages, and chemical compositions to infer formation environments and history.

Rocks are typically classified by origin and composition: igneous rocks by silica content and degree of fractionation (felsic to ultramafic), metamorphic rocks by metamorphic grade and index minerals, and sedimentary rocks by texture and composition. This classification underpins the broader rock cycle, which describes how rocks are created, transformed, transported, and recycled within the Earth.

Petrology informs natural-resource exploration, geothermal and groundwater studies, and assessments of geological hazards, and it provides essential constraints on models of crustal and mantle evolution. The field developed from mineralogy and crystallography in the 18th–20th centuries, with advances in petrography, geochemistry, and experimental petrology shaping modern practice.