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	Coesite - Wikipedia, the free encyclopedia
		Coesite is a form of silicon dioxide that is formed when very high pressure (2–3 gigapascals) and moderately high temperature (700 °C) are applied to quartz.
		The presence of coesite in unmetamorphosed rocks may be evidence of a meteorite impact event or of an atomic bomb explosion.
		The molecular structure of coesite consists of four silicon dioxide tetrahedra arranged in a ring.
	en.wikipedia.org /wiki/Coesite (265 words)

	Coesite: Encyclopedia topic (Site not responding. Last check: 2007-10-18)
		Coesite is a form of silicon dioxide (silicon dioxide: A white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechartelierite) that is formed when very high pressure (2–3 gigapascal (gigapascal: the gigapascal, symbol gpa is an si unit of pressure....
		The presence of coesite is taken as evidence of an earth impact event (impact event: more facts about this subject) or an atomic bomb (atomic bomb: A nuclear weapon in which enormous energy is released by nuclear fission (splitting the nuclei of a heavy element like uranium 235 or plutonium 239)) explosion.
		The molecular structure of coesite consists of four silicon dioxide tetrahedra (tetrahedra: a tetrahedron (plural: tetrahedra) is a polyhedron composed of four triangular...
	www.absoluteastronomy.com /reference/coesite (307 words)

	LASER RAMAN MICROPROBE IDENTIFICATION OF COESITE IN KYANITE ECLOGITES AND THEIR HOST GNEISSES, NORTH-EAST GREENLAND ...
		Coesite inclusions have been unambiguously identified by laser Raman spectroscopy in zircon from kyanite-eclogites and their quartzofeldspathic host gneisses that are exposed on a small island in Jøkelbugt (78°00’N, 18°04’W) off the northeast coast of Greenland.
		The UHP mineral assemblage in the kyanite eclogites is garnet + omphacite + kyanite + phengite + coesite + rutile.
		Coesite in the host gneisses demonstrates unequivocally that a coherent slab of the Laurentian continental margin experienced UHP conditions during the Caledonian collision with Baltica.
	gsa.confex.com /gsa/2004AM/finalprogram/abstract_80242.htm (501 words)

	Coesite Eclogite SRV-1
		This is a grain of coesite in an eclogite I collected in South Africa in 1975.
		The gray is coesite, and the mottled gray rim is polycrystalline quartz.
		Twinned coesite grain at extinction in crossed polars with polycrystalline quartz rim.
	ruby.colorado.edu /~smyth/Research/Images/SRV-1/SRV-1.html (844 words)

	Bayerisches Geoinstitut - Annual Report 2002 - Microstructure of metamorphic coesite from Dora Maira, Alps (F. ...
		The presence of relic coesite indicates that the metamorphic host rock was subducted to depths greater than 100 km, at peak metamorphic conditions of 3.7 GPa and 800 °C. The coesite occurs as inclusions in garnets and is surrounded by a rim of retrograde quartz, displaying usually a palisade structure.
		The Burgers vectors of dislocations in monoclinic coesite are [100], [001], [110] (i.e.
		The quartz veins are aligned parallel to (100) and (021) composition planes of rotation twins in coesite.
	www.bgi.uni-bayreuth.de /annual_report/2002/c_61.phtml (431 words)

	Eclogite - Wikipedia, the free encyclopedia
		Glaucophane and titanite form in eclogite as pressures decrease during exhumation of the rocks, or may be earlier formed minerals that did not entirely react away.
		Eclogites in granulite terranes are known from the Musgrave Block of central Australia where a continental collision took place at 550-530 Ma, resulting in burial of rocks to >45km (15 kilobars) and rapid (in less than 10 million years!) exhumation via thrust faults prevented significant melting.
		Felsic rocks in these terranes contain sillimanite, kyanite, coesite, orthoclase and pyroxene, and are rare, peculiar rocks formed by an unusual tectonic event.
	en.wikipedia.org /wiki/Eclogite (1079 words)

	Meteoritical Impact Materials
		It was the mineral Coesite, named after it's discover, Loring Coes, that finally convinced the scientific community that the diamonds found in the Canyon Diablo meteorite resulted from the pressure of impact.
		Coes had clearly demonstrated that pressures and temperatures necessary for the transformation of quartz to coesite were at least 20,000 atmospheres and 700 to 1700 degrees C. Meteoritic impact was the only natural event that could provide this.
		In 1960, coesite was identified as an abundant mineral in the sheared Coconino sandstone of Meteor Crater.
	www.meteorlab.com /Frame01/ktimpact.htm (388 words)

	Kaghan
		Coesite, recognized petrographically and confirmed by in situ Raman microprobe spectroscopy, is reported from an eclogite from the Kaghan valley, Pakistan, and represents the first record of ultrahigh pressure metamorphism in the Himalaya.
		The coesite occurs as inclusions in omphacite (the largest grain is 70 _m) and shows the characteristic breakdown to radiating (palisade texture) quartz as well as the typical radiating network of fractures in the host pyroxene (Fig.
		The possibility that some degree of tectonic overpressure led to coesite formation, and therefore that depths were much shallower, is negated by the fact that the whole mineral assemblage of the eclogite yields pressures within the stability field of coesite.
	www.geo.uni-potsdam.de /mitarbeiter/OBrien/Kaghan/kaghan.html (3180 words)

	COESITE (Silicon Dioxide)
		Both quartz and coesite are polymorphs with all the members of the Quartz Group which also include cristobalite, tridymite and stishovite.
		Now the presence of coesite and stishovite is diagnostic evidence of a meteor impact when craters of unknown origin are examined.
		Coesite has also been identified in kimberlites where other high pressure minerals such as diamond are found.
	mineral.galleries.com /minerals/silicate/coesite/coesite.htm (380 words)

	8th INTERNATIONAL KIMBERLITE CONFERENCE (8IKC)
		The banding and occurrences of symplektite intergrowths of garnet with kyanite and coesite characterize eclogites with mosaic structure.
		Three varieties of coesite are detected: a) subhedral coesite grains with the size 1.0-3.0 mm; b) coesite inclusions in the rockforming minerals; c) subgraphic intergrowths with garnet.
		The presence and preservation of coesite in eclogites indicate both high pressure of their formation (more than 30 kbar) and set a number of limitations on the timing of xenoliths cooling while their trapping and elevating on the surface.
	www.venuewest.com /8IKC/s6post.htm (8483 words)

	Essentials of Geology : Feature Article 6.1
		Researchers then began to use the presence of coesite and stishovite as a "litmus test" for determining if strange circular structures on Earth were made as a result of meteor impact.
		Numerous such structures, defined by circular faults and circular igneous intrusions, had been discovered, but they did not have the bowl-shaped depression and raised rim characteristic of lunar meteor craters, and so their origin remained a subject of debate—some geologists thought they might be a consequence of volcanic explosions.
		If it is true, then we should be able to find a widely distributed layer of debris containing coesite and stishovite at the level in a stratigraphic sequence at which many fossil species became extinct.
	www.wwnorton.com /earth/egeo/features/ch6_1.htm (448 words)

	Bryson Burke Diamond Corporation: Diamond Exploration and Mining in Canada
		Coesite, formerly known only from impact craters, has been found in rocks that were once at the surface (first found in 1984).
		Coesite (SiO2) is a high pressure variant of the mineral quartz.
		However, if the coesite is enclosed within a garnet grain (as an inclusion), there is sometimes insufficient room forthe coesite to invert to the less-dense quartz: the rigid garnet acts like a pressure-vessel.
	brysonburke.com /coesite_in_high_mountains.html (301 words)

	Coesite eclogites abstract
		Coesite (or pseudomorphic quartz) is more common than previously recognized in the eclogite xenolith suite from the Roberts Victor Mine, South Africa.
		All coesite eclogites in this study (eighteen samples) are classified as Group I, and have mineral compositions that span virtually the entire compositional range of Group I eclogites described from this locality.
		These observations are consistent with a model in which protoliths of these rocks were oceanic basalts and intrusive rocks that underwent exchange with seawater at relatively low temperatures, to variable extents, prior to subduction and metamorphism to eclogite facies, without suffering significant partially melting during or following subduction.
	www.geology.utoronto.ca /faculty/schulze/coesite_abstract.html (225 words)

	Structures - Crystallography Laboratory at Virginia Tech
		It is from a crystal of coesite, a high-pressure polymorph of SiO2.
		Coesite is found in a few metamorphic rocks which have been buried to depths of more than 100km in the Earth.
		When the fractional coordinates are combined with the lattice parameters that define the size and shape of the unit-cell, we can calculate the distances between the atoms, or the bond lengths.
	www.ccp14.ac.uk /ccp/web-mirrors/ross-angel/crystal/structure.html (759 words)

	Alpine notes - Metamorphism - coesite (Site not responding. Last check: 2007-10-18)
		Most silica at the earth's surface is in the form of quartz.
		But under high pressures (equivalent to depths in the earth in excess of 80 km), the stable form of silica is the mineral coesite.
		The garnet crystal has acted as a protective pressure vessel so that pieces of coesite have been preserved to the earth's surface.
	earth.leeds.ac.uk /alps/metamorphism/coesite.htm (122 words)

	Coesite, Stishovite, Diamonds, Tektites, Impact Metamophism, and Related Features
		Without any real proof impact theory was mostly considered mostly as a curious phenomenon associated with other planets, and as a science meteorite study did not advance until the mid 1900's.
		The discovery of Coesite in the early 1950's marked the turning point in meteorite study by bringing about the general acceptance of impact cratering.
		Coesite had never been found in any naturally occurring rock, until close examination of the Coconino sandstone within the Arizona (Barringer or Meteorite) crater in the 1950's.
	www.umich.edu /~gs265/meteor.htm (3630 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		The frequencies of the vibrations are related to the structure and chemistry of the mineral.
		For quartz, coesite, and stishovite, the composition is identical (SiO2); however, the mineral structure differs from one polymorph to another.
		Coesite (monoclinic, C2/c) has a = 7.15 symbol 68 \f "WP MathA" \s 10D and c = 7.18 symbol 68 \f "WP MathA" \s 10D with a unit cell volume of 548.76 symbol 68 \f "WP MathA" \s 10D3.
	epswww.unm.edu /iom/pubs/Lane31LPSC.doc (1310 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		We have done this for the coesite « quartz transformation by comparing the textures generated during transformation of a synthetic coesite "rock" to textures found in exhumed, ultrahighpressure (UHP) rocks, either within regional metamorphic terranes or as kimberlitic xenoliths.
		A spectacular feature of the transformation in nature is the occurrence of "palisade quartz," a texture composed of elongate quartz crystals which grew perpendicular to the contact of relict coesite with another phase.
		Moreover, during the earliest stages of the transformation, quartz nucleates on coesite grain boundaries and grows perpendicular to the interface between coesite crystals in a manner similar to the palisade texture.
	pangea.stanford.edu /~jed/Abstracts/AGU95C.html (484 words)

	RELICT COESITE EXSOLUTION IN OMPHACITE FROM WESTERN TIANSHAN ECLOGITES, CHINA
		Relict coesite exsolution lamellae or rods in omphacite have been identified in eclogites from western Tianshan, China.
		Compared with the standard spectrum of coesite, the intensity of diagnostic band 521 Cm-1 of coesite exsolution in omphacite from Western Tianshan eclogites is not stronger.
		The second stage from coesite to quartz may happen at 2.7~2.8 Gpa and near 600OC whicth is consistent with the calculation of Omp-Gt-Phen geothermometer and equilibrium grids of magnesite-bearing eclogite (Zhang et al., 2002a; b).
	gsa.confex.com /gsa/2003AM/finalprogram/abstract_63475.htm (535 words)

	AGU94 (Site not responding. Last check: 2007-10-18)
		Knowledge of the kinetics of the coesite to quartz transformation is essential to constraining the range of possible P-T-t paths which allow the preservation of coesite in ultrahighpressure metamorphic rocks exhumed to the surface.
		We are conducting pistoncylinder experiments to measure the rate and determine the mechanism of the transformation as a function of P, T, and DG (i.e., the amount of pressure understep).
		In partially transformed samples, the host coesite crystals are enveloped by quartz neoblasts, separated from each other by high angle, highlyincoherent grain boundaries.
	pangea.stanford.edu /~jed/Abstracts/AGU94.html (344 words)

	IngentaConnect Carbonate-Bearing UHPM Rocks from the Tso-Morari Region, Ladakh, ... (Site not responding. Last check: 2007-10-18)
		Evidence of ultrahigh-pressure metamorphism (UHPM) of subducted Indian continental crust in the form of carbonate-bearing coesite eclogite is preserved in the Tso-Morari Crystalline Complex (TMC) in eastern Ladakh, India.
		Coesite, magnesite, and dolomite occur as inclusions in zoned garnet.
		At ultrahigh-pressure (27 kbar) and a temperature of 650°C, quartz transforms to coesite.
	www.ingentaconnect.com /content/bell/igr/2003/00000045/00000001/art00004 (250 words)

	The influence of OH in coesite on the kinetics of the coesite-quartz phase transition -- Lathe et al. 90 (1): 36 -- ...
		The influence of OH in coesite on the kinetics of the coesite-quartz phase transition -- Lathe et al.
		The influence of OH in coesite on the kinetics of the coesite-quartz phase transition
		Metastable coesite is an important pressure indicator for ultrahigh-pressure
	ammin.geoscienceworld.org /cgi/content/abstract/90/1/36 (247 words)

	Untitled Document
		At high pressures quartz is replaced by its higher density polymorph, coesite.
		At even higher pressures coesite is replaced by stishovite.
		Both coesite and stishovite would require the pressures equivalent to those in the Earth's mantle in order to form.
	faculty.sulross.edu /jlwstark/planet/planet54.html (828 words)

	Auburn University Geology Department Virtual Field Trips Wetumpka Impact Structure
		The presence of two shock indicators, coesite and stishovite, in quartz-rich rocks have aided in the positive identification of impact craters.
		Coesite and stishovite are mineral pseudomorphs of quartz that form at extremely high pressures.
		Volcanic explosions cannot reach the pressures needed to form coesite and stishovite (greater than 15 and 30 GPa, respectively) (Melosh, 1989).
	www.auburn.edu /academic/science_math/geology/docs/gen.htm (1084 words)

	An experimental study into the rheology of synthetic polycrystalline coesite aggregates
		Coesite has been found as a relic in ultrahigh pressure metamorphic (UHPM) crust worldwide and is expected to play a major role in the mechanical behavior of continental crust at UHPM conditions.
		Extrapolation of the experimental data to natural conditions cannot be constrained by comparison with natural microstructures, due to the lack of preserved coesite other than as single crystal inclusions.
		Citation: Renner, J. Stöckhert, A. Zerbian, K. Röller, and F. Rummel (2001), An experimental study into the rheology of synthetic polycrystalline coesite aggregates, J.
	www.agu.org /pubs/crossref/2001/2001JB000431.shtml (355 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		at 1044 K for coesite and stishovite polymorphs of silica was carried out to determine the enthalpy of the coesite-stishovite transition.
		These experiments were performed on high-purity, single-phase samples of coesite and stishovite.
		Using these new data, we have calculated the equilibrium phase boundary between coesite and stishovite and obtained a slope, dP/dT=0.0031 (2) GPa/ K. This calculated slope is in good agreement with that determined [0.0026(2) GPa/K] from the in-situ X-ray diffraction study of Zhang et al.
	navrotsky.engr.ucdavis.edu /abstracts/PCM-23-96-11.html (164 words)

	Research - Crystallography Laboratory at Virginia Tech
		These small changes in structure under pressure will have a large effect on cation partitioning between phases within the Earth, will influence the retention and diffusion rates of non-bonded species such as the rare gases that are important for isotope geochemistry, and will determine the elastic properties of these minerals.
		Both coesite and feldspars display complex variation of their volume under compression, but this can be explained in terms of the response of frameworks being that of essentially rigid tetrahedra.
		The compression of some Si-O bonds in coesite serves only to modify the rigid-unit behaviour of the framework.
	www.crystal.vt.edu /crystal/research.html (780 words)

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