Petrology is the branch of geology that studies the origin, composition,
distribution and structure of rocks. 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 and tested chemically when needed.
Methodology Petrology utilizes the classical fields
of mineralogy, petrography, optical mineralogy, and chemical analysis to
describe the composition and texture of rocks. Modern 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.
Branches There are three branches of petrology,
corresponding to the three types of rocks: igneous, metamorphic, and
sedimentary, and another dealing with experimental techniques:
Igneous petrology focuses on the composition and texture of igneous
rocks. Igneous rocks include volcanic and plutonic rocks.
Sedimentary petrology focuses on the composition and texture of sedimentary
rocks. Metamorphic petrology focuses on the
composition and texture of metamorphic rocks
Experimental petrology employs high-pressure, high-temperature
apparatus to investigate the geochemistry and phase relations of
natural or synthetic materials at elevated pressures and temperatures.
Experiments are particularly useful for investigating rocks of the lower crust
and upper mantle that rarely survive the journey to the surface in pristine
condition. They are also one of the prime sources of information about
completely inaccessible rocks such as those in the Earth's lower mantle and in
the mantles of the other terrestrial planets and the Moon. The work of
experimental petrologists has laid a foundation on which modern understanding
of igneous and metamorphic processes has been built.
See also Important publications in petrology
Ore References
Best, Myron G., Igneous and Metamorphic Petrology. ISBN 1-4051-0588-7
Blatt, Harvey; Tracy, Robert J.; Owens, Brent, Petrology: igneous, sedimentary,
and metamorphic. ISBN 978-0-7167-3743-8 Dietrich, Richard Vincent; Skinner,
Brian J., Gems, Granites, and Gravels: knowing and using rocks and minerals.
ISBN 978-0-521-10722-8 Fei, Yingwei; Bertka, Constance M.;
Mysen, Bjorn O., Mantle Petrology: field observations and high-pressure
experimentation. ISBN 0-941809-05-6 Philpotts, Anthony; Ague, Jay,
Principles of Igneous and Metamorphic Petrology. ISBN 978-0-521-88006-0
Robb, L., Introduction to Ore-Forming Processes. ISBN 978-0-632-06378-9
External links Atlas of Igneous and metamorphic rocks,
minerals, and textures - Geology Department, University of North Carolina
Metamorphic Petrology Database - Department of Earth and Environmental
Sciences, Rensselaer Polytechnic Institute
Petrological Database of the Ocean Floor - Center for International Earth Science
Information Network, Columbia University