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Geology

Rheid

In geology, a rheid is a substance whose temperature is below the melting point and whose deformation by viscous flow during the time of observation is at least three orders of magnitude ((10^3)) greater than the elastic deformation under the given conditions. A material is a rheid by virtue of the time of observation. The term, coined […]

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Neptunism

Neptunism is a theory established at the end of the eighteenth century, especially thanks to the work of the German geologist Abraham Gottlob Werner, according to which all rocks had a marine origin. The etymology is related to Neptune, in Roman mythology the god of water and sea. According to this theory, the center of the

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Plutonism

Plutonism is a theory proposed by the Scottish geologist James Hutton in the second half of the eighteenth century, according to which, in the processes generating rocks, should be taken into account also the magmatic ones, that is attributable to the “subterranean heat”. The name derives from Pluto, the ancient deity of Roman mythology, lord of

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Basalt

Basalt is an effusive rock of volcanic origin, dark or black in color with a relatively low silica (SiO2) content (45 to 52% by weight). Basalt consists primarily of calcic plagioclase and pyroxenes; some basalts may also be rich in olivine. The intrusive correspondent of basalt is gabbro. Basalt can range in appearance from porphyritic to

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Petrology

Petrology (from Ancient Greek πέτρος (pétros) ‘rock’, and λόγος (lógos) ‘account, explanation, narrative’) or rock science, is a geological discipline, which through the use of investigations of various kinds (especially mineralogical, crystallographic, geochemical and chemical-isotopic), deals essentially with problems (physical, chemical and biological) inherent in the genesis and parentage of rocks. The petrological investigation is carried

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Seismology

Seismology (from the greek seismos = earthquake and logos = word) is the branch of geophysics that studies seismic phenomena, in particular earthquakes and the propagation of elastic waves (and inelastic) generated by them (seismic waves), also interested in the study of events such as tidal waves and in general areas of instability of the Earth,

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Ablation

The term ablation can be used to refer to the process by which the surface layers of an object are eroded or vaporized. Examples include friction (e.g., a spacecraft entering the Earth’s atmosphere) and radiation (e.g., tumors removed by laser). The term is often found in space physics associated with atmospheric re-entry, glaciology, medicine, and passive fire

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Metasomatism

Metasomatism is a metamorphic process in which a rock or part of a rock, while remaining in a solid state, is pervasively altered by the introduction or removal of chemical components as a result of its interaction with aqueous fluids (solutions). The term is derived from the Greek μετά (meta = beyond, beyond) and σώματος

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Field [mineral deposit]

In geology, the term “field” refers to a mineral deposit containing a metal or other valuable resources in a cost-competitive concentration. It is usually used in the context of a mineral deposit from which it is convenient to extract its metallic component. The deposits are exploited by mining in the case of solid mineral deposits (such as iron or coal)

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Petrography

Petrography is the branch of petrology that describes in detail the rocks, their minerals and textures. Petrography describes the appearance of rocks, their mineralogical composition, and, most importantly, their structure on a microscopic scale. It is a valuable aid in geodynamic scale interpretations of regional geology and in palynological reconstructions, and is essential in the analysis

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Crystal habit

Crystalline habit is defined as the typical appearance of crystals determined by the relative development of the faces and the prevalence of one or more characteristic simple geometric shapes. The main conditions that can influence growth are: Crystals have a discontinuous and periodic three-dimensional structure, they are formed by particles (leptons) arranged at regular intervals

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Crystal

In mineralogy and crystallography, a crystal (from the greek κρύσταλλος, krýstallos, ice) is defined as the atomic or molecular structure that matter in the solid state presents, chemically and physically homogeneous. In other words atoms, molecules or ions have a regular three-dimensional geometric arrangement, which is repeated indefinitely in the three spatial dimensions, called crystal lattice or

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Earthquake

In geophysics, earthquakes (from Latin: terrae motus, which means “movement of the earth”), also called seisms or telluric tremors (from Latin Tellus, Roman goddess of the Earth), are vibrations or settlements of the Earth’s crust, caused by the sudden displacement of a rock mass in the subsoil. This displacement is generated by the forces of tectonic nature

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Metamorphism

In mineralogy and petrology metamorphism is defined as the set of mineralogical and/or structural transformations in the solid state that a rock undergoes when it is found, underground, in physical and chemical environments different from those in which it originated. The factors that determine metamorphism are changes in temperature and pressure (lithostatic and oriented or stress) and

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Mineralogy

Mineralogy is the science that studies the chemical composition, crystal structure, and physical properties (such as hardness, magnetism, and optical properties) of minerals, as well as their formation, transformation, and use by humans. The classification and nomenclature of minerals is codified by the International Mineralogical Association (IMA), which consists of various organizations representing mineralogists in

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Perovskite

Perovskite (discovered in the Ural Mountains of Russia by Gustav Rose in 1839 and is named after Russian mineralogist Lev Perovski 1792–1856) is a calcium titanium oxide mineral composed of calcium titanate (CaTiO3). Its name is also applied to the class of compounds which have the same type of crystal structure as CaTiO3 \((^{\textrm{XII}}\textrm{A}^{2+\textrm{VI}}\textrm{B}^{4+}\textrm{X}^{2-}_3)\), known

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