Petrology

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Petrology (from Greek: ¿¿¿¿¿, petra, rock; and ¿¿¿¿¿, logos, knowledge) is the branch of geology that studies rocks, and the conditions in which rocks form. Lithology once was approximately synonymous with petrography, but in current usage, lithology is a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with microscopic details. In the oil industry, lithology, or more specifically mud logging, is the graphic representation of geological formations being drilled through, and drawn on a log called a mud log. As the cuttings are circulated out of the borehole they are sampled, examined (typically under a 10x microscope) and tested chemically when needed.