petrograafia

Petrograafia, or petrography, is the branch of geology that studies rocks by describing their minerals, textures, and structures in hand specimens and in prepared thin sections viewed under polarized light. The aim is to classify rocks and to interpret their origin, history, and the processes that formed them. Petrography integrates mineralogy, petrology, and microscopy to provide a detailed description of rock composition and fabric.

Practices include macroscopic hand specimen description, the preparation and analysis of rock thin sections, and quantitative modal analysis through point counting. In igneous petrography, mineral percentages and textures are used alongside classification diagrams (such as QAPF) to distinguish rock types. In sedimentary petrography, emphasis is placed on grain composition, cement, clast roundness and sorting, and diagenetic features. In metamorphic petrography, mineral assemblages and index minerals reveal pressure–temperature conditions and metamorphic history.

Subfields of petrography cover igneous, sedimentary, and metamorphic rocks, often integrating with geochemistry and mineralogy. Applications span mining and mineral exploration, evaluation of construction materials, petroleum reservoir characterization, and academic research. Petrography provides essential context for understanding a rock’s formation, alteration, and its role within larger geological settings.

Modern petrography relies on a range of tools, including the petrographic microscope for thin-section analysis, scanning electron microscopy, X-ray diffraction, electron microprobes, and cathodoluminescence. These techniques enable precise mineral identification, texture analysis, and microstructural interpretation, contributing to broader geological and engineering insights.