In geology, petrology (from Greek: πέτρα, petra, rock; and λόγος, logos, knowledge)'s the study of rocks, and the conditions in which they form. Lithology once was approximately synonymous with petrography, but in current usage, lithology's a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks, while petrography's the speciality that deals with microscopic details. In the oil industry, lithology, or… (More on Petrology)