In geology Geology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed. The field is a major academic discipline, and is also, rock is a naturally occurring solid aggregate of minerals A mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific chemical composition. Minerals range in composition and/or mineraloids A mineraloid is a mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amorphous glass and not a crystal. Jet is derived from decaying wood under extreme pressure. Opal is another mineraloid because.
The Earth's outer solid layer, the lithosphere The lithosphere is the rigid outermost shell of a rocky planet, is made of rock. In general rocks are of three types, namely, igneous Igneous rock is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma (molten rock) being cooled and becoming solid. They may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be, sedimentary Sedimentary rock is one of the three main rock types . Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution. The processes that form sedimentary rock occur at the surface of the Earth and within bodies of water. Rock formed from sediments covers 75-80% of the, and metamorphic Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic. The scientific study of rocks is called petrology Petrology 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, and petrology is an essential component of geology.
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Rock classification
The rocky side of a mountain creek near Orosí Orosi is a town in the Cartago Province in Costa Rica, about 30 kilometers south of the capital San José. Orosi is situated on the Reventazón River in the Orosi Valley. The cultivation of coffee is the leading industry in the area. Orosi has a population of approximately 4,600 and has the oldest Catholic church still in use in Costa Rica. The, Costa Rica Costa Rica, officially the Republic of Costa Rica is a country in Central America, bordered by Nicaragua to the north, Panama to the east and south, the Pacific Ocean to the west and south and the Caribbean Sea to the east.Rocks are classified by mineral and chemical A chemical substance is a material with a specific chemical composition composition, by the texture Texture in geology refers to the physical appearance or character of a rock, such as grain size, shape, arrangement, and pattern at both the megascopic or microscopic surface feature level. This includes the geometric aspects and relations amongst the component particles or crystals which is called the crystallographic texture or preferred of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous Igneous rock is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma (molten rock) being cooled and becoming solid. They may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be, sedimentary Sedimentary rock is one of the three main rock types . Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution. The processes that form sedimentary rock occur at the surface of the Earth and within bodies of water. Rock formed from sediments covers 75-80% of the and metamorphic Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic. They are further classified according to particle size Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which is the size of a single crystal inside the particles or grains. A single grain can be composed of. The transformation of one rock type to another is described by the geological model called the rock cycle The rock cycle is a fundamental concept in geology that describes the dynamic transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. As the diagram to the right illustrates, each type of rock is altered or destroyed when it is forced out of its equilibrium conditions. An igneous rock such as.
Sample of igneous gabbro Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline massIgneous rocks Igneous rock is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma (molten rock) being cooled and becoming solid. They may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be are formed when molten magma Magma is molten rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma often collects in a magma chamber inside a volcano. Magma is capable of intrusion into adjacent rocks, extrusion onto the surface as lava, and cools and are divided into two main categories: plutonic rock An intrusion is any formation of intrusive igneous rock; rock formed from magma that cools and solidifies within the crust of a planet. In contrast, an extrusion consists of extrusive rock; rock formed above the surface of the crust and volcanic A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface. The word volcano is derived from the name of Vulcano island off Sicily which in turn, was named after Vulcan, the Roman god of fire. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth Earth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density. It is also referred to as the World, the Blue Planet,[note 3] and Terra.[note 4]'s crust (example granite Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Outcrops of granite tend to), while volcanic or extrusive rocks result from magma reaching the surface either as lava Lava is molten rock expelled by a volcano during eruption. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at temperatures from 700 °C to 1,200 °C . Although lava is quite viscous, with about 100,000 times the viscosity of water, or fragmental ejecta (examples pumice Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid cooling and rapid depressurization. The depressurization and basalt Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey) .[1]
Sandstone with iron oxide bandsSedimentary rocks Sedimentary rock is one of the three main rock types . Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution. The processes that form sedimentary rock occur at the surface of the Earth and within bodies of water. Rock formed from sediments covers 75-80% of the are formed by deposition of either clastic Clastic rocks are composed of fragments, or clasts, of pre-existing rock. The term is most commonly, but not uniquely, applied to sedimentary rocks sediments Sediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited, organic matter, or chemical precipitates (evaporites Evaporites are water-soluble mineral sediments that result from the evaporation of bodies of surficial water. Evaporites are considered sedimentary rocks), followed by compaction of the particulate matter and cementation during diagenesis In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original. Sedimentary rocks form at or near the Earth's surface. Mud rocks comprise 65% (mudstone, shale Shale is a fine-grained, clastic sedimentary rock composed of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by thin laminae or parallel layering or bedding less than one centimeter in thickness and siltstone Siltstone is a sedimentary rock which has a composition intermediate in grain size between the coarser sandstones and the finer mudstones and shales); sandstones Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form 20 to 25% and carbonate rocks 10 to 15% (limestone Limestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record. Calcium (along with nitrogen, phosphorus, and potassium) is a key mineral to plant nutrition: soils overlying limestone bedrock tend to be pre-fertilized and dolostone Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is resistant to erosion and can either contain bedded layers).[1]
Banded gneissMetamorphic rocks Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic are formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature In physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics. If no net heat flow occurs between two objects, the objects have the same temperature; otherwise heat flows and pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the Earth's surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation Recrystallization is a physical process that has meanings in chemistry, metallurgy and geology).[1]
The three classes of rocks — the igneous, the sedimentary and the metamorphic — are subdivided into many groups. There are, however, no hard and fast boundaries between allied rocks. By increase or decrease in the proportions of their constituent minerals they pass by every gradation into one another, the distinctive structures also of one kind of rock may often be traced gradually merging into those of another. Hence the definitions adopted in establishing rock nomenclature merely correspond to selected points (more or less arbitrary) in a continuously graduated series.[2]
Impact on society
Rocks have had a huge impact on the cultural and technological advancement of the human race. Rocks have been used by Homo sapiens A human is a member of a species of bipedal primates in the family Hominidae . Mitochondrial DNA and fossil evidence indicates that modern humans evolved in east Africa about 200,000 years ago. When compared to other animals and primates, humans have a highly developed brain, capable of abstract reasoning, language, introspection and problem and other hominids A number of known extinct genera are grouped with humans in the Hominina subtribe, others with orangutans in the Ponginae subtribe. The most recent common ancestor of the Hominidae lived some 13 million years ago, when the ancestors of the orangutans speciated from the ancestors of the other three genera.[citation needed] The ancestors of the for more than 2 million years Lower Paleolithic (genus Homo). Lithic technology In archeology, lithic technology refers to a broad array of techniques and styles to produce usable tools from various types of stone. The earliest stone tools were recovered from modern Ethiopia and were dated to between two-million and three-million years old. The archaeological record of lithic technology is divided into three major time marks some of the oldest and continuously used technologies. The mining Mining is the extraction of valuable minerals or other geological materials from the earth, usually from an ore body, vein or seam. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash. Any material that cannot be grown through agricultural processes, or of rocks for their metal In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations); those ions are surrounded by delocalized electrons, which are responsible for the conductivity. The solid thus produced is held by electrostatic interactions between the ore An ore is a type of rock that contains minerals such as gemstones or metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals such as gold or content has been one of the most important factors of human advancement, which has progressed at different rates in different places in part because of the kind of metals available from the rocks of a region.
The prehistory and history of civilization is classified into the Stone Age The Stone Age is a broad prehistoric time period during which humans widely used stone for toolmaking, Bronze Age, and Iron Age. Although the stone age has ended virtually everywhere, rocks continue to be used to construct buildings and infrastructure. When so used, rocks are called dimension stone.
See also
- Dimension stone
- Geologic time scale
- Geomorphology
- Kekur
- List of rock types
- List of rocks in Western Australia
- Oldest rock
- Quarry
- Rauk
- Riprap
References
- ^ a b c Blatt, Harvey and Robert J. Tracy, 1996, Petrology, W. H. Freeman, 2nd ed. ISBN 0-7167-2438-3
- ^ This article incorporates text from the article "Petrology" in the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.
Categories: Petrology | Rocks | Materials
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Fri, 07 Aug 2009 09:50:37 GM
The Grand Canyon would belong on a top ten list of world . geologic. wonders, not just the US. However, I must point out the two billion year old . rock. exposed at the bottom of the canyon is the Vishnu schist. Schist is a metamorphic . rock. , ...
Q. I really like geology, because I like to study animals
Asked by Jason R - Wed Jul 30 20:17:36 2008 - - 5 Answers - 0 Comments
A. lol no
Answered by brandon - Wed Jul 30 20:23:00 2008
