Petrology is a fundamental branch of geology that mainly deals with the compositions, structures, and evolution of different rocks that constitutes our mother earth and other planets of our solar system. Rocks are the solidified manifestations of different geological materials, generated within/on the earth and preserve a great deal of information that quests the petrologists to unravel and interpret that information. Petrologic studies involve fieldwork and geological mapping to understand the complex field relationships between different kinds of rocks such as igneous, sedimentary, and metamorphic. The collection of different rock types holds a great deal in petrological sciences, which provides direct observation of physical characteristics of the rocks. A subdiscipline of petrology is petrography, which deals specifically with the description and classification of rocks. Petrologic research involves petrography, typically involving the examination of rock slices at high magnification. So, petrologic research is a hybrid science that involves aspects of chemistry, mineralogy, physics, geological mapping, and sometimes biology. Progressing research and innovating technology in the field of petrology have led budding petrologists to unravel the complexity hindered in their formational history. Integrated field and laboratory investigations are being carried out on different earth materials for a better understanding of planet Earth. Considering that minerals, sediments, rocks, meteorites, soils, and fluids are essentially chemical compounds, the principles and analytical methods of chemistry can be directly applied to understand the behavior and evolution of the earth. Additionally, the study of petrology is crucial for the discovery and development of mineral resources. Developing mineral deposits requires an understanding of rocks because of their intimate association with ore deposits, oil, and natural gas.

Geochemistry

As one of the important branches of geology, geochemistry lets us know the fundamental knowledge about the origin, occurrence, and distribution of different chemical elements in varied compositional earth materials and rocks, which constitute the crust, mantle, and core of the Earth and the entire cosmic system. Geochemistry holds a high position in unraveling the complex early evolutionary history of the earth and its contemporary planets in one of the largest known solar systems. This subject will facilitate us to understand the composition of the atmosphere, hydrosphere, and lithosphere and their continual interaction. The cyclic transfer of the different elements among these phases of the earth can be understood by knowing the principles that govern their distribution. Geochemistry also provides the basic and advanced working principle of sophisticated geochemical instruments (XRF, ICPMS, XRD, EPMA, etc.) and their capability to measure the different concentrations of elements. Chemical procedures that have to be followed to analyze the rock, soil samples, and water samples will also be known from the study of geochemistry. The utility of geochemistry has also extended to study the actual composition of the soil, water, and atmospheric constituents, continuous interactions, and consequent chemical modifications. Knowing the concentration of major, minor, and trace elemental concentrations of the rocks can establish the probable composition of source magmas from which a rock has been formed. Simultaneously, able to construct the physico-chemical conditions under which minerals and rocks were formed. Sophisticated geochemical instruments, analytical techniques, and chemical procedures help us constrain the probable age of the rocks and their corresponding tectono magmatic history. Geochemistry also allows us to know how mass elemental transfer happens among the different lithofacies of the globe and its tectonic control. Often, geochemistry plays a key role in the exploration and prospecting of various mineral and metal deposits, which are hidden beneath surface. Making use of the fundamental chemistry principles, geochemistry permits us to identify the valuable mineral/ore deposits, which are of economic importance. Advancement in geochemical analytical procedures with greater data precision support geochemists to examine and evaluate the formational conditions of various rock materials and associated mineral deposits.   

It has been shown that all naturally occurring elements are composed of (1) stable isotopes whose abundance varies as a function of melting, crystallization, and temperature-dependent exchange processes; and (2) radioactive and radiogenic isotopes whose abundance varies due to radioactive decay. Geochronology is the widely used application of radioactive isotopes: determining the age of rocks, sediments, and geologic events, including Earth's and our solar system's ages.

Petrology and geochemistry have a close relationship with each other and are one of the current thrust disciplines of geological research. This combination includes field and experimental studies of the evolution of rocks under varying temperatures, pressure, and fugacities of oxygen, carbon dioxide, and water. All the geochemical research based on major, minor, trace elements, stable and radiogenic isotopes, including geochronological analyses, is of great potential in revealing tectonic plate interactions, metallogeny, and many other geological phenomena. The modern and important techniques of seismic tomography, have shown us the internal activities of the mantle, where ascending magmas related to mantle plumes and hot spots and descending material reflect old sunken oceanic lithospheric slabs, portrayed as deep as the very interface mantle/core, greatly modifying our previous conceptions of "simple" mantle convection into a more complex scheme.