Metamorphic rock in the context of Volcanic rock

In geology, a rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's outer solid layer, the crust, and most of its interior, except for the liquid outer core and pockets of magma in the asthenosphere. The study of rocks involves multiple subdisciplines of geology, including petrology and mineralogy. It may be limited to rocks found on Earth, or it may include planetary geology that studies the rocks of other celestial objects.

Rocks are usually grouped into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rocks are formed when magma cools in the Earth's crust, or lava cools on the ground surface or the seabed. Sedimentary rocks are formed by diagenesis and lithification of sediments, which in turn are formed by the weathering, transport, and deposition of existing rocks. Metamorphic rocks are formed when existing rocks are subjected to such high pressures and temperatures that they are transformed without significant melting.

Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character.

Most continental crust is dry land above sea level. However, 94% of the Zealandia continental crust region is submerged beneath the Pacific Ocean, with New Zealand constituting 93% of the above-water portion.

Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedimentation is any process that causes these particles to settle in place. Geological detritus originates from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus is formed by bodies and parts (mainly shells) of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies (marine snow). Sedimentation may also occur when dissolved minerals precipitate from water solution.

The sedimentary rock cover of the continents of the Earth's crust is extensive (73% of the Earth's current land surface), but sedimentary rock is estimated to be only 8% of the volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding. Sedimentary rocks are often deposited in large structures called sedimentary basins. Sedimentary rocks have also been found on Mars.

Feldspar (/ˈfɛl(d).ˌspɑːr/ FEL(D)-spar; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust and 41% of the Earth's continental crust by weight.

Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rocks.

Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO₃) or dolomite (CaMg(CO₃)₂) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is typically not foliated (layered), although there are exceptions.

In geology, the term marble refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone.

Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression.

The foliation in slate, called "slaty cleavage", is caused by strong compression in which fine-grained clay forms flakes to regrow in planes perpendicular to the compression. When expertly "cut" by striking parallel to the foliation with a specialized tool in the quarry, many slates display a property called fissility, forming smooth, flat sheets of stone which have long been used for roofing, floor tiles, and billiard tables. Slate is frequently grey in color, especially when seen en masse covering roofs. However, slate occurs in a variety of colors even from a single locality; for example, slate from North Wales can be found in many shades of grey, from pale to dark, and may also be purple, green, or cyan. Slate is not to be confused with shale, from which it may be formed, or schist.

Lapis lazuli (UK: /ˌlæpɪs ˈlæz(j)ʊli, ˈlæʒʊ-, -ˌli/; US: /ˈlæz(j)əli, ˈlæʒə-, -ˌliˌ læˈzuːli/) is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. Its name originates from the Persian word for the gem, lāžward, and serves as the root for the word for "blue" in several languages, including Spanish and Portuguese azul and English azure. Lapis lazuli is a rock composed primarily of the minerals lazurite, pyrite, diopside, and calcite. As early as the 7th millennium BC, lapis lazuli was mined in the Sar-i Sang mines, in Shortugai, and in other mines in Badakhshan province in modern northeast Afghanistan. Lapis lazuli artifacts, dated to 7570 BC, have been found at Bhirrana, which is the oldest site of Indus Valley Civilisation. Lapis was highly valued by the Indus Valley Civilisation (3300–1900 BC). Lapis beads have been found at Neolithic burials in Mehrgarh, the Caucasus, and as far away as Mauritania. It was used in the funeral mask of Tutankhamun (1341–1323 BC).

By the end of the Middle Ages, Europe began importing lapis lazuli to grind it into powder and make ultramarine pigment. Ultramarine was used by some of the most important artists of the Renaissance and Baroque, including Masaccio, Perugino, Titian and Vermeer; it was often reserved for the clothing of the central figures of their paintings, especially the Virgin Mary. Ultramarine has also been found in dental tartar of medieval nuns and scribes, perhaps as a result of licking their painting brushes while producing medieval texts and manuscripts.

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. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. 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. Modern sedimentary petrology is making increasing use of chemistry.

Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava.

The magma can be derived from partial melts of existing rocks in a terrestrial planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses.

In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment. Then, the rock was buried underneath subsequent rock and was subjected to high pressures and temperatures, causing the rock to recrystallize. The overall composition of a metasedimentary rock can be used to identify the original sedimentary rock, even where they have been subject to high-grade metamorphism and intense deformation.

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO₃), and dolomite rock (also known as dolostone), which is composed of dolomite (CaMg(CO₃)₂). They are usually classified on the basis of texture and grain size. Importantly, carbonate rocks can exist as metamorphic and igneous rocks, too. When recrystallized carbonate rocks are metamorphosed, marble is created. Rare igneous carbonate rocks even exist as intrusive carbonatites and, even rarer, there exists volcanic carbonate lava.

Carbonate rocks are also crucial components to understanding geologic history due to processes such as diagenesis in which carbonates undergo compositional changes based on kinetic effects. The correlation between this compositional change and temperature can be exploited to reconstruct past climate as is done in paleoclimatology. Carbonate rocks can also be used for understanding various other systems as described below.

Hadean zircon is the oldest-surviving crustal material from the Earth's earliest geological time period, the Hadean eon, about 4 billion years ago. Zircon is a mineral that is commonly used for radiometric dating because it is highly resistant to chemical changes and appears in the form of small crystals or grains in most igneous and metamorphic host rocks.

Hadean zircon has very low abundance around the globe because of recycling of material by plate tectonics. When the rock at the surface is buried deep in the Earth it is heated and can recrystallise or melt. In the Jack Hills, Australia, scientists obtained a relatively comprehensive record of Hadean zircon crystals in contrast to other locations. The Jack Hills zircons are found in metamorphosed sediments that were initially deposited around 3 billion years ago, or during the Archean Eon. However, the zircon crystals there are older than the rocks that contain them. Many investigations have been carried out to find the absolute age and properties of zircon, for example the isotope ratios, mineral inclusions, and geochemistry of zircon. The characteristics of Hadean zircons show early Earth history and the mechanism of Earth's processes in the past. Based on the properties of these zircon crystals, many different geological models were proposed.

In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover".

Basement rock consists of continental crustal rock which has been modified several times through tectonic events including deformation, metamorphism, deposition, partial melting and magmatism.

Schist (/ˈʃɪst/ SHIST) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced schistosity (named for the rock). This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates. This texture reflects a high content of platy minerals, such as mica, talc, chlorite, or graphite. These are often interleaved with more granular minerals, such as feldspar or quartz.

Schist typically forms during regional metamorphism accompanying the process of mountain building (orogeny) and usually reflects a medium grade of metamorphism. Schist can form from many different kinds of rocks, including sedimentary rocks such as mudstones and igneous rocks such as tuffs. Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a mica schist). Where the type of the original rock (the protolith) is discernible, the schist is usually given a name reflecting its protolith, such as schistose metasandstone. Otherwise, the names of the constituent minerals will be included in the rock name, such as quartz-felspar-biotite schist.

Gneiss (/naɪs/ NYSE) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F). Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.

Gneisses are common in the ancient crust of continental shields. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss.