William O. answered • 04/10/19
B.S. in Geochemistry from Brown University
Yes, Petrology and Lithology are different branches of geology. The study of Petrology is a branch of geochemistry which seeks to find how rocks are formed at a chemical level, whether that be through volcanism, crystallization, metamorphic reactions, or other processes, studying especially crystallization rates, diffusion, thermal properties, enthalpy and gibbs free energy, etc. For example, my senior thesis was an experimental petrology study in which I attempted to emulate the conditions several miles beneath mid-ocean ridges in a laboratory environment on a microscopic scale to gain insight into melt-rock interactions which altered the chemical and mineral composition of the oceanic crust. As far as lithology is concerned, I've never heard it used as a term for a specific branch of geology, but rather as a term for the characteristics of rocks at outcrop scale. For example, the "lithology" of an area could refer to the bedding, faults, general composition, and metamorphic features. If, indeed, there is such a branch of geology, I would imagine it would be largely focused on field work, structure, and hypothesizing the origin of rocks and land-forms at outcrop-to-regional scale. If you have any other questions, feel free to DM me.
