Petrology

naturally occurring solid aggregate of one or more minerals or mineraloids

rock formed by the deposition of material

upright=1.35|thumb|The Permian through [[Jurassic strata of the Colorado Plateau area of southeastern Utah demonstrate the principles of stratigraphy.]] Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy (stratigraphy by age).

thumb|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.]]

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landform created by the eruption of mud or slurries, water and gases

Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand-sized specimens. The most important petrographer's tool is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin se

thumb|Quartz-filled geode, shown from inside (top) and outside (bottom)

upright=1.35|thumb|Samples of soapstone

thumb|right|340px|Lapilli on Kilauea

thumb|Ptygmatic folding in migmatite on Naissaar Island, Estonia thumb|Migmatite on the coast of Saaremaa, Estonia thumb|Intricately-folded migmatite from near Geirangerfjord, Norway

thumb|upright=1.3|Cross section (geometry)|Cross section of a laccolith intruding into and deforming strata

thumb|Eolianite carbonate facies (Holocene) on [[Long Island, Bahamas]]

thumb|upright|Soil with broken rock fragments overlying bedrock at Reay|Sandside Bay, Caithness, Scotland thumb|Soil profile with bedrock labeled R

piece or sample of soil from the Moon

thumb|Concretions in Torysh, Western [[Kazakhstan]] thumb|Concretions with lens shape from island in Vltava river, Prague, Czech Republic thumb|Marlstone aggregate concretion, [[Sault Ste. Marie, Michigan, United States]] A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word concretion is borrowed from Latin , itself derived from concrescere , from con- and crescere .

time-consuming transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous

thumb|Kerogen can be found in oil shale

thumb|right|Vein skeleton of a Hydrangea leaf showing anastomoses of veins

thumbnail|Basalt Mafic is a term used in geology to describe silicate minerals, magmas, and igneous rocks that are rich in magnesium and iron, while being relatively low in silica content. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian.

thumb|Limescale build-up inside a pipe reduces both liquid flow through the pipe and thermal conduction from the liquid to the outer pipe shell. Both effects will reduce the pipe's overall thermal efficiency when used as a heat exchanger.

thumb|Modern ooids from a beach on Joulter Cays, The Bahamas, with 0.5 mm scale thumb|right|Ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah thumb|right|Thin-section of calcitic ooids from an oolite within the Carmel Formation (Middle [[Jurassic) of southern Utah]]

magmatic rock formed below the surface

geological term for a type of fracture in rock

sheetlike body within a rock

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Lithification (from the Ancient Greek word lithos meaning 'rock' and the Latin-derived suffix -ific) is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithification is a process of porosity destruction through compaction and cementation. Lithification includes all the processes which convert unconsolidated sediments into sedimentary rocks. Petrifaction, though often used as a synonym, is more specifically used to describe the replacement of organic material by silica in the formation of fossils.

any material trapped inside a mineral during its formation

repetitive layering in metamorphic rocks

thumb|upright=1.3|The Permian through [[Jurassic lithostratigraphy of the Colorado Plateau area of southeastern Utah that makes up much of the famous prominent rock formations in protected areas such as Capitol Reef National Park and Canyonlands National Park. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area, Utah.]

classification system for igneous rocks

In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Molten felsic magma and lava is more viscous than molten mafic magma and lava. Felsic magmas and lavas have lower temperatures of melting and solidification than mafic magmas and lavas.

geological term for the mass of material in which larger grains, crystals or clasts are embedded

massive volcanic formation resulting from flood basalt eruptions

cylindrical section of a naturally occurring substance, usually obtained by drilling into it with special drills

structural geology

thumb| Basic types of intrusions: 1. Laccolith 2. Small dike 3. [[Batholith 4. Dike 5. Sill 6. Volcanic neck, pipe 7. Lopolith As a general rule, in contrast to the smoldering volcanic vent in the figure, these names refer to the fully cooled and usually millions-of-years-old rock formations, which are the result of the underground magmatic activity shown.]] A lopolith is a large igneous intrusion which is lenticular in shape with a depressed central region. Lopoliths are generally concordant with the intruded strata with dike or funnel-shaped feeder bodies below the body. The term was first d

thumb|right|Melange from Geology of Narooma|Narooma, [[Australia.]]

theoretical and applied science of the mechanical behavior of rock and rock masses; compared to geology

chemical elements or compounds with low boiling points associated with planet’s or moon’s crust or atmosphere

zone of variably metamorphosed (ultra)mafic volcanic sequences with associated sedimentary rocks occurring in Archaean and Proterozoic cratons between granite and gneiss bodies, typically dozens to thousands of kilometres long

A ventifact (also wind-faceted stone, windkanter) is a rock that has been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. The word "Ventifact" is derived from the Latin word "Ventus" meaning 'wind'. These geomorphic features are most typically found in arid environments where there is little vegetation to interfere with aeolian particle transport, where there are frequently strong winds, and where there is a steady but not overwhelming supply of sand.

Anatexis (via Latin from Greek roots meaning 'to melt down') is the partial melting of rocks. Traditionally, anatexis is used specifically to discuss the partial melting of crustal rocks, while the generic term "partial melting" refers to the partial melting of all rocks, in both the crust and mantle.

thumb|right|250 px|Typical sial material, a Precambrian [[granite from St. Francois Mountains, Missouri, showing the potassium feldspar (felsic) matrix]]

A protolith () is the original, unmetamorphosed rock from which a given metamorphic rock is formed.

matter of Earth's oceanic crust, consisting of rocks rich in magnesium silicate minerals

thumb|Modern ooids from a beach on Joulter Cays, The Bahamas. thumb|Ooids on the surface of limestone; Carmel Formation (Middle [[Jurassic) of southern Utah, USA.]] thumb|A thin slice of calcitic ooids from the Carmel Formation, Middle Jurassic, of southern Utah, USA.

thumb|Spherulites in volcanic ash|rhyolitic ash, Hailstone Trail, Echo Canyon, [[Chiricahua Mountains, Arizona]] thumb|Spherulite markings on snowflake obsidian thumb|thin section|Photomicrograph of [[rhyolite, showing spherulitic texture (brown, between grey to white crystals)]]

Paragenesis, in petrology, is the formation sequence of minerals in an ore deposit. It is used in studies of igneous and metamorphic rock genesis and importantly in studies of the hydrothermal deposition of ore minerals and the rock alteration (vein metasomatism) associated with ore mineral deposits. The concept and application of paragenesis, meaning 'born beside' in Greek, was first applied by August Breithaupt in 1849 in his work Die Paragenesis der Mineralien.

term in geology

type of rock body

upright=1.35|thumb|right|Stylolites in limestone

well-formed crystal with sharp and well developed faces

size, shape and mutual relations of the particles of a rock

area of younger rock completely surrounded by older rocks

thumb|Close-up of granite, a phanerite rock, from [[Yosemite National Park in California, U.S.]] thumb|Phaneritic diorite from Massachusetts

thumb|"Hammerstone" eolith, recognized to be of natural origin by Boule in 1905 An eolith (from Ancient Greek ἠώς (ēṓs), meaning "dawn", and λίθος (líthos), meaning "stone") is a flint nodule that appears to have been crudely knapped. Eoliths were once thought to have been artifacts, the earliest stone tools, but are now believed to be geofacts (stone fragments produced by fully natural geological processes such as glaciation).

distribution of crystallographic orientations of a polycrystalline sample

thumb|300px|Perthitic textures: antiperthite (1), perthite (2), and mesoperthite (3)