petrográfiai

Petrográfiai, or petrography, is the branch of geology that describes and interprets rocks by examining their mineral composition, texture, and fabric. The practice relies on optical mineralogy and thin-section analysis, typically using a petrographic microscope to study rocks in transmitted light with polarized light. Through thin sections, geologists identify minerals, determine their arrangement, understand crystal sizes and shapes, pleochroism, birefringence, and extinction angles, and infer how the rock formed and evolved.

Rock types are investigated across the igneous, metamorphic, and sedimentary categories. Petrography uses classification schemes such as the QAPF diagram for felsic igneous rocks and modal analysis to quantify mineral proportions. Textures and microstructures reveal processes such as crystallization, deformation, metamorphism, diagenesis, and sedimentary sorting. Modern petrography integrates with geochemistry, X-ray diffraction, electron microprobe analysis, and imaging techniques to constrain formation conditions, temperature, pressure, and post-formational history.

Historically, petrography developed in the 19th century with advances in optical mineralogy and the routine use of polished and thin sections. The name derives from Greek words petro, rock, and graphia, writing, reflecting the descriptive nature of the discipline. The plural form petrográfiai appears in some languages to denote the field or its subfields.

Applications span academic research, mineral exploration, petrology, and engineering geology, where rock description supports interpretation of earth history and resource potential.