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Gneiss 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. Gneiss forms at higher temperatures and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.
Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust. Kyanite is also known as disthene or cyanite.
Titanite, or sphene (from the Greek sphenos (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly replaced by thorium.
In geology, rock 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.
Metamorphism is the transformation of existing rock to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface.
Petrology is the branch of geology that studies rocks 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.
Coesite is a form (polymorph) of silicon dioxide (SiO2) that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (700 °C, 1,300 °F), are applied to quartz. Coesite was first synthesized by Loring Coes, Jr., a chemist at the Norton Company, in 1953.
Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% magnesium oxide (MgO). It is classified as a 'picritic rock'. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.
Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within crust and mantle of a rocky planetary body, such as the Earth. It is important in the formation of igneous rocks because it is one of the main processes of magmatic differentiation. Fractional crystallization is also important in the formation of sedimentary evaporite rocks.
Alfred Edward "Ted" Ringwood FRS FAA was an Australian experimental geophysicist and geochemist, and the 1988 recipient of the Wollaston Medal.
Ekhard Karl Hermann Salje, FRS is an Emeritus Professor, and formerly Professor of Mineralogy and Petrology and Head of the Department of Earth Sciences, Cambridge University.
Schreyerite (V2Ti3O9), is a vanadium, titanium oxide mineral found in the Lasamba Hill, Kwale district in Coast Province, Kenya. It is polymorphous with kyzylkumite.
In geology ultrahigh-temperature metamorphism (UHT) is extreme crustal metamorphism with metamorphic temperatures exceeding 900 °C. Granulite-facies rocks metamorphosed at very high temperatures were identified in the early 1980s, although it took another decade for the geoscience community to recognize UHT metamorphism as a common regional phenomenon. Petrological evidence based on characteristic mineral assemblages backed by experimental and thermodynamic relations demonstrated that Earth's crust can attain and withstand very high temperatures (900–1000 °C) with or without partial melting.
Friedrich Alfred Seifert is a German mineralogist and geophysicist. He is the founding director of Bayerisches Geoinstitut at University of Bayreuth. A silicate mineral, seifertite, is named after him.
A whiteschist is an uncommon metamorphic rock formed at high to ultra-high pressures. It has the characteristic mineral assemblage of kyanite + talc, responsible for its white colour. The name was introduced in 1973 by German mineralogist and petrologist Werner Schreyer. This rock is associated with the metamorphism of some pelites, evaporite sequences or altered basaltic or felsic intrusions. Whiteschists form in the MgO–Fe
2O
3–Al
2O
3–SiO
2–H
2O (MFASH) system. Rocks of this primary chemistry are extremely uncommon and they are in most cases thought to be the result of metasomatic alteration, with the removal of various mobile elements.
Professor Somnath Dasagupta was the vice-chancellor of Assam University till 13 November 2015 and professor of metamorphic geology at Indian Institutes of Science Education and Research, Kolkata.
Hans Peter Eugster was a Swiss-American geochemist, mineralogist, and petrologist.
A petrogenetic grid is a geological phase diagram that connects the stability ranges or metastability ranges of metamorphic minerals or mineral assemblages to the conditions of metamorphism. Experimentally determined mineral or mineral-assemblage stability ranges are plotted as metamorphic reaction boundaries in a pressure–temperature cartesian coordinate system to produce a petrogenetic grid for a particular rock composition. The regions of overlap of the stability fields of minerals form equilibrium mineral assemblages used to determine the pressure–temperature conditions of metamorphism. This is particularly useful in geothermobarometry.
Cornelio August Severinus Doelter, Doelter y Cisterich or Cisterich y de la Torre was a Caribbean born Austrian geologist who specialized in chemical mineralogy and petrology, serving as a professor at the Universities of Graz and Vienna. He conducted pioneering experiments in synthetic mineralogy and petrology by melting down rocks and allowing recrystallization of mineral constituents.
The German Mineralogical Society is a non-profit German society for the promotion of mineralogy. It has about 1400 members (2021) and belongs to the International Mineralogical Association and the umbrella organization for geosciences. It was founded at the meeting of German natural scientists and physicians in Cologne in 1908 based on a proposal by Friedrich Martin Berwerth at the 1907 meeting in Dresden.
References
- ↑ "People in the News" (PDF). Elements. 3 (6): 376. December 2007.
- ↑ "IN MEMORIAM Werner Schreyer (1930–2006)" (PDF). International Mineralogical Association. Archived from the original (PDF) on 13 October 2011. Retrieved 5 November 2023.
- ↑ Maresch, Walter; Grew, Edward; Seifert, Friedrich (2008). "From field observation to experimental petrology and back: A special issue to honour Werner Schreyer Preface". European Journal of Mineralogy. 20 (5): 691–692. Bibcode:2008EJMin..20..691M. doi:10.1127/0935-1221/2008/0020-1884.
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