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Cementation (geology)
Cementation involves ions carried in groundwater chemically precipitating to form new crystalline material between sedimentary grains. The new pore-filling minerals forms "bridges" between original sediment grains, thereby binding them together. In this way, ''sand'' becomes sandstone, and ''gravel'' becomes conglomerate or breccia. Cementation occurs as part of the diagenesis or lithification of sediments. Cementation occurs primarily below the water table regardless of sedimentary grain sizes present. Large volumes of pore water must pass through sediment pores for new mineral cements to crystallize and so millions of years are generally required to complete the cementation process. Common mineral cements include calcite, quartz, and silica phases like cristobalite, iron oxides, and clay minerals; other mineral cements also occur. Cementation is continuous in the groundwater zone, so much so that the term "zone of cementation" is sometimes used interchangeably. Cementati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cristobalite
Cristobalite is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group, which also include coesite, tridymite and stishovite. It is named after Cerro San Cristóbal in Pachuca Municipality, Hidalgo, Mexico. It is used in dentistry as a component of alginate impression materials as well as for making models of teeth. Properties Metastability Cristobalite is stable only above 1470 °C, but can crystallize and persist metastably at lower temperatures. The persistence of cristobalite outside its thermodynamic stability range occurs because the transition from cristobalite to quartz or tridymite is "reconstructive", requiring the breaking up and reforming of the silica framework. These frameworks are composed of Si O4 tetrahedra in which every oxygen atom is shared with a neighbouring t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sedimentology
Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures. Sedimentary rocks cover up to 75% of the Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata. The premise that the processes affecting the earth today are the same as in the past is the basis for determining how sedimentary features in the rock record were formed. By comparing similar features today to features in the rock record—for example, by comparing modern sand dunes to dunes preserved in ancient aeolian sandstones—geologists reconstruct past environmen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Society For Microbiology
The American Society for Microbiology (ASM), originally the Society of American Bacteriologists, is a professional organization for scientists who study viruses, bacteria, fungi, algae, and protozoa as well as other aspects of microbiology. It was founded in 1899. The Society publishes a variety of scientific journals, textbooks, and other educational materials related to microbiology and infectious diseases. ASM organizes annual meetings, as well as workshops and professional development opportunities for its members. History ASM was founded in 1899 under the name the "Society of American Bacteriologists." In December 1960, it was renamed the "American Society for Microbiology." Mission ASM's mission is "to promote and advance the microbial sciences." The society seeks to accomplish this mission through: * Publishing highly-cited publications * Running multi-disciplinary meetings * Deploying resources and expertise around the world * Advocating for scientific research * Fost ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sporosarcina Pasteurii
''Sporosarcina pasteurii'' formerly known as ''Bacillus pasteurii'' from older taxonomies, is a gram positive bacterium with the ability to precipitate calcite and solidify sand given a calcium source and urea; through the process of microbiologically induced calcite precipitation (MICP) or biological cementation. ''S. pasteurii'' has been proposed to be used as an ecologically sound biological construction material. Researchers studied the bacteria in conjunction with plastic and hard mineral; forming a material stronger than bone. It is a commonly used for MICP since it is non-pathogenic and is able to produce high amounts of the enzyme urease which hydrolyzes urea to carbonate and ammonia. Physiology ''S. pasteurii'' is a gram positive bacterium that is rod-like shaped in nature. It has the ability to form endospores in the right environmental conditions to enhance its survival, which is a characteristic of its bacillus class. It has dimensions of 0.5 to 1.2 microns in wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hardgrounds
Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone sequences and distinguished from later-lithified sediments by evidence of exposure to normal marine waters. This evidence can consist of encrusting marine organisms (especially bryozoans, oysters, barnacles, cornulitids, hederelloids, microconchids and crinoids), borings of organisms produced through bioerosion, early marine calcite cements, or extensive surfaces mineralized by iron oxides or calcium phosphates (Palmer, 1982; Bodenbender et al., 1989; Vinn and Wilson, 2010; Vinn and Toom, 2015). Modern hardgrounds are usually detected by sounding in shallow water or through remote sensing techniques like side-scan sonar. Carbonate hardgrounds often host a unique fauna and flora adapted to the hard surface. Organisms usually cement ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Capillary Action
Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a biological cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid. Etymology Capillary comes from the Latin word capillaris, meaning "of or resembling hair." The meaning stems from the tiny, hairlike diameter of a capillary. While capilla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beachrock
Beachrock is a friable to well-cemented sedimentary rock that consists of a variable mixture of gravel-, sand-, and silt-sized sediment that is Cementation (geology), cemented with Calcium carbonate, carbonate minerals and has formed along a shoreline. Depending on location, the sediment that is cemented to form beachrock can consist of a variable mixture of Seashell, shells, coral fragments, rock fragments of different types, and other materials. It can contain scattered Artifact (archaeology), artifacts, pieces of wood, and coconuts. Beachrock typically forms within the intertidal zone within tropical or semitropical regions. However, Quaternary beachrock is also found as far north and south as 60° latitude.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. Scholle, P.A., D.G. Bebout, and C.H. Moore (1983) ''Carbonate Depositional Environments.'' Memoir no. 33. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Folk Classification
The Folk classification, in geology, is a technical descriptive classification of sedimentary rocks devised by Robert L. Folk, an influential sedimentary petrologist and Professor Emeritus at the University of Texas. Folk's sandstone (clastic) classification Folk's philosophy is that the name of a rock must convey as much information as possible without being a complete description. For this, he proposed five important properties of sandstones to use as defining characteristics. These five properties are: grain size, chemically precipitated cements, textural maturity, miscellaneous transported constituents, and clan designation. Folk's fivefold name must be in the following format: :(Grain size): (chemically precipitated cements) (textural maturity) (miscellaneous transported constituents) (clan designation) However, Folk stated that cements and miscellaneous transported constituents are optional categories as they are not always observed. The other three properties should always ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clay Mineral
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals form in the presence of water and have been important to life, and many theories of abiogenesis involve them. They are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing. Properties Clay is a very fine-grained geologic material that develops plasticity when wet, but becomes hard, brittle and non–plastic upon drying or firing. It is a very common material, and is the oldest known ceramic. Prehistoric humans discovered the useful properties of clay and used it for making pottery. The chemistry of clay, including its capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility. Because the individual particles in clay are less than ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iron Oxide
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron oxides and oxyhydroxides are widespread in nature and play an important role in many geological and biological processes. They are used as iron ores, pigments, catalysts, and in thermite, and occur in hemoglobin. Iron oxides are inexpensive and durable pigments in paints, coatings and colored concretes. Colors commonly available are in the "earthy" end of the yellow/orange/red/brown/black range. When used as a food coloring, it has E number E172. Stoichiometries Iron oxides feature as ferrous ( Fe(II)) or ferric ( Fe(III)) or both. They adopt octahedral or tetrahedral coordination geometry. Only a few oxides are significant at the earth's surface, particularly wüstite, magnetite, and hematite. * Oxides of FeII ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation from α-quartz to β-quartz takes place abruptly at . Since the transformation is accompanied by a significant change in volume, it can easily induce microfracturing of ceramics or rocks passing through this temperature threshold. There are many different varieties of quartz, several of which are classified as gemstones. Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. Quartz is the mineral defining the val ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
