Petrology Petrology Petrology (from the Greek πέτρος, "pétros", "rock" and λόγος, "lógos", "subject matter", see -logy) is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together because they both contain heavy use of chemistry, chemical methods, and phase diagrams. Sedimentary petrology is, on the other hand, commonly taught together with stratigraphy because it deals with the processes that form sedimentary rock. Lithology was once approximately synonymous with petrography, but in current usage, lithology focuses on macroscopic hand-sample or outcrop-scale
Experimental petrology are analyzed - qualities of interest include mineral assemblage (which minerals crystallized and how much), mineral chemistry, and liquid (the remainder of the synthetic magma base) composition. Equilibrium crystallization studies are those in which a starting liquid is cooled until fully crystalline. This is taken to be the "equilibrium state" of the composition under those particular P/T conditions. Criticisms of equilibrium crystallization include the observation that real-world systems are believed to rarely sit still during crystallization and thus would not be able to properly equilibrate. Fractional crystallization studies represent a fairly recent trend in experimental petrology, gaining popularity as a