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A thin section of a volcanic sand grain seen under the microscope, with plane-polarized light in the upper picture, and cross-polarized light in the lower picture. Scale box is 0.25 mm.

Petrology (from Ancient Greek πέτρος (pétros) 'rock', and -λογία (-logía) 'study of') is the branch of geology that studies rocks, their mineralogy, composition, texture, structure and the conditions under which they form.[1] Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology.[2] Igneous and metamorphic petrology are commonly taught together because both make heavy use of chemistry, chemical methods, and phase diagrams. Sedimentary petrology is commonly taught together with stratigraphy because it deals with the processes that form sedimentary rock.[3] Modern sedimentary petrology is making increasing use of chemistry.


Lithology was once approximately synonymous with petrography, but in current usage, lithology focuses on macroscopic hand-sample or outcrop-scale description of rocks while petrography is the speciality that deals with microscopic details.

In the petroleum 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 10× microscope) and tested chemically when needed.


Ljudmila Dolar Mantuani (1906–1988), first female professor of petrography in Yugoslavia

Petrology utilizes the fields of mineralogy, petrography, optical mineralogy, and chemical analysis to describe the composition and texture of rocks. Petrologists also include the principles of geochemistry and geophysics through the study of geochemical trends and cycles and the use of thermodynamic data and experiments in order to better understand the origins of rocks.


There are three branches of petrology, corresponding to the three types of rocks: igneous, metamorphic, and sedimentary, and another dealing with experimental techniques:

See also



  1. ^ The 22nd edition of the Manual of mineral science. Buch. New York: Wiley. 2002. p. 1. ISBN 978-0-471-25177-4.
  2. ^ Blatt, Harvey; Tracy, Robert J.; Owens, Brent E. (2006). Petrology: igneous, sedimentary and metamorphic (3rd ed.). New York: Freeman. ISBN 978-0-7167-3743-8.
  3. ^ Frost, B. R.; Frost, C. D. (2014). Essentials of Igneous and Metamorphic Petrology. Cambridge University Press.
  4. ^ a b Winter, John D. (2010). Principles of igneous and metamorphic petrology (2nd ed.). New York: Prentice Hall. pp. 467–468. ISBN 978-0-321-59257-6.