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Topic: Omphacite

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	Omphacite - Wikipedia, the free encyclopedia
		Omphacite is a member of the pyroxene group of silicate minerals with formula: (Ca,Na)(Mg,Fe,Al)Si It is a variably deep to pale green or nearly colorless variety of augite and represents an intermediate composition between the calcium rich augite and the sodium rich jadeite.
		It is also found in Marin and Sonoma counties of California.
		The name omphacite derives from the Greek omphax or unripe grape for the typical green color.
	en.wikipedia.org /wiki/Omphacite (249 words)

	Eclogite - Wikipedia, the free encyclopedia
		The fresh rock can be striking in appearance, with red to pink garnet (almandine-pyrope) in a green matrix of sodium-rich pyroxene (omphacite).
		Eclogite Facies is determined by the temperature and pressure conditions required to metamorphose basaltic rocks to an eclogite assemblage.
		Eclogite is a rare and important rock because it is formed only by conditions typically found in the mantle or the lowermost part of thickened continental crust.
	en.wikipedia.org /wiki/Eclogite (1086 words)

	Na-Pyroxene
		Omphacite generally has a nondescript light green color, and low-order nterference colors.
		Omphacite is light green and may show faint pleochroism; jadeite is generally colorless but may be very pale green or yellow.
		Omphacite has considerably lower birefringence (maximum colors are upper first or second order).
	www.und.nodak.edu /instruct/mineral/320petrology/opticalmin/napyrox.htm (794 words)

	Engebøfjellet rutile deposit, Mineralogy (Site not responding. Last check: 2007-10-24)
		Eclogite paragenesis comprises garnet, omphacite, amphibole, phengite, clinozoisite, quartz, dolomite, rutile and pyrite.
		Abundant eclogite-facies veining (quartz, omphacite, garnet, carbonate, phengite...) indicate that the fluid pressure was high during this event.
		Retrogression of the eclogites is often seen dependant on both deformation and fluid infiltration and occurred predominantly along shear zones and margins of the lens.
	www.ngu.no /industrimineraler/engebofjellet/7-Mineralogy.html (701 words)

	Fluid backflow
		Inclusions of omphacite in garnet, glaucophane and epidote.
		Towards the rim of garnet inclusions of paragonite, omphacite and rutile are the main inclusions.
		Omphacite apparent in the matrix and replaced by glaucophane and/or epidote in addition with omphacite included in garnet indicates a retrogressive p-t path from the eclogite facies back to the blueschist facies.
	www.min.uni-kiel.de /petrographie/schenk/projekte/fluide/fluidbackflow.html (539 words)

	GIA: Newsroom: News Release Details
		A small number of rough and polished specimens of a new dark blue omphacite, sold as “blue jade,” were seen at the February Tucson shows.
		Omphacite, like jadeite, is a member of the pyroxene group.
		Electron-microprobe analyses of a fourth blue cabochon revealed that it was composed predominantly of omphacite.
	www.gia.edu /newsroom/wd_608ar_19725_news_release_details.cfm (447 words)

	696
		In general, the paragenesis of the eclogites is garnet + omphacite + phengite + quartz + zoisite ± kyanite + rutile + apatite + zircon ± sphene.
		The extremely light oxygen is found in the Qinglongshan eclogite, with dO values being -9.2 to -9.3” for omphacite**, -9.8 to -10.1” for garnet, -8.5 to -9.0” for kyanite, and -8.8 to -8.9” for phengite.
		The isotopic geothermometry for quartz-mineral pairs yields a temperature range from 550 to 750°C, which is close to the petrological temperatures of 600 to 800°C derived from cation partitioning between coexisting phases.
	www.the-conference.com /JConfAbs/1/696.html (878 words)

	P-T path from symplectites (Site not responding. Last check: 2007-10-24)
		Eclogites of basaltic composition consist mainly of garnet and omphacite, a sodium-rich pyroxene.
		A symplectite colony nucleates on a grain boundary between two omphacite grains and grows into the grain on one side.
		The pyroxene in the colony retains structural continuity with the omphacite grain on the other side of the boundary.
	www.earth.ox.ac.uk /~davewa/research/symplectites.html (1094 words)

	Kaghan
		The garnets have conspicuous darker cores and are within a weakly defined foliation defined by elongate omphacite (0.5-1.5 mm and dusted with rutile inclusions), white mica (0.5-1 mm), aggregates of quartz, and chains of rutile (partly rimmed by titanite).
		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.
		Omphacite is Jd25-33 (Aeg4-13 from charge balance) but individual grains appear to be unzoned.
	www.geo.uni-potsdam.de /mitarbeiter/OBrien/Kaghan/kaghan.html (3180 words)

	RELICT COESITE EXSOLUTION IN OMPHACITE FROM WESTERN TIANSHAN ECLOGITES, CHINA
		Raman spectra analyses show the presence of quartz exsolution at the diagnostic bands of 468 and 131 Cm-1 and their host omphacite with the bands of 1023, 680 and 224 Cm-1 in Western Tianshan eclogites, which are consistent with their mineral microprobe analyses.
		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.
		That means the precursor of quartz exsolution in omphacite was coesite which changed into quartz during late retrograde metamorphism.
	gsa.confex.com /gsa/2003AM/finalprogram/abstract_63475.htm (535 words)

	Eclogite (Site not responding. Last check: 2007-10-24)
		Eclogite is a dense, green plutonic rock composed of coarse grains of green, sodium-rich pyroxene (omphacite) and pale pink, magnesium rich garnet (almandite and pyrope); kyanite and rutile are also common.
		It occurs as small bodies or blocks that appear to have been formed in the lowermost crust and upper mantle, where igneous and metamorphic processes merge.
		Common minerals are: garnet, quartz, omphacite pyroxene, and sometimes kyanite, phengite, paragonite, zoisite, dolomite, and corundum.
	www.seismo.berkeley.edu /~jill/wisc/eclogite.html (102 words)

	IngentaConnect Prograde and Retrograde P-T Paths of the Late Paleozoic Glaucopha... (Site not responding. Last check: 2007-10-24)
		Late Paleozoic glaucophane eclogite and garnet glaucophane schist are intercalated with pelitic schist from the Omi eclogitic unit in the Renge metamorphic belt, Hida Mountains, southwestern Japan.
		In the foliated matrix, the eclogite-facies mineral assemblage garnet + omphacite + glaucophane + epidote + rutile + quartz + phengite is partly replaced by secondary minerals such as chlorite, titanite, albite, and calcite, which coexist with recrystallized glaucophane.
		value between garnet and omphacite, and a significant increase in jadeite component of omphacite suggest a rise in both temperature and pressure during prograde eclogitization.
	www.ingentaconnect.com /content/bell/igr/2002/00000044/00000009/art00004 (480 words)

	Coesite Eclogite SRV-1
		The trace OH contents of the phases have been measured (Rossman et al 1990), and this omphacite is the most hydrous ever reported (Smyth et al 1991).
		The sanidine grain at lower left is thought to be a sanidine pseudomorph after K-cymrite (KAlSi3O8 2H2O) and a source for water during decompression.
		Smyth (1980) Cation vacancies and the crystal chemistry of breakdown reactions in kimberlitic omphacites.
	ruby.colorado.edu /~smyth/Research/Images/SRV-1/SRV-1.html (844 words)

	First evidence for ultrahigh-pressure metamorphism of eclogites in Pohorje, Slovenia: Tracing deep continental ...
		Polycrystalline quartz inclusions surrounded by radial fractures in garnet, omphacite, and kyanite are interpreted to be pseudomorphs after coesite.
		Abundant quartz rods and needles in omphacite indicate an exsolution from a preexisting supersilicic clinopyroxene that contained a Ca-Eskola component.
		Geothermobarometry on the mineral assemblage garnet + omphacite + kyanite + phengite + quartz/or coesite yields peak pressure and temperature conditions of 3.0–3.1 GPa and 760°–825°C, well within the stability field of coesite, thus supporting the microtextural evidence for UHP metamorphism.
	www.agu.org /pubs/crossref/2004/2004TC001641.shtml (387 words)

	IngentaConnect Chain multiplicity faults in deformed omphacite from eclogite (Site not responding. Last check: 2007-10-24)
		Deformed and recovered omphacite from an eclogite sample of the Lower Schist Cover of the Tauern Window was studied by conventional and high resolution transmission electron microscopy.
		The CMFs are usually intercalations of one or two double chains parallel to (010) in the single chain omphacite.
		The frequent occurrence of CMFs in omphacite suggests that 1/2[011](010) is an important slip system which is probably responsible for lattice preferred orientation.
	www.ingentaconnect.com /content/schweiz/ejm/2004/00000016/00000001/art00005 (248 words)

	Coexisting retrograde jadeite and omphacite in a jadeite-bearing lawsonite eclogite from the Motagua Fault Zone, ...
		Coexisting retrograde jadeite and omphacite in a jadeite-bearing lawsonite eclogite from the Motagua Fault Zone, Guatemala -- Tsujimori et al.
		Coexisting retrograde jadeite and omphacite in a jadeite-bearing lawsonite eclogite from the Motagua Fault Zone, Guatemala
		Coexisting jadeite and omphacite were found as retrograde minerals
	ammin.geoscienceworld.org /cgi/content/abstract/90/5-6/836 (202 words)

	Learn About Clinopyroxenes Page. Quartz 'N' All - High Quality Crystals, Minerals and Fossils
		Below you will find the geological properties and some further information regarding Clinopyroxenes.These include Diopside, Augite, pigeonite, hedenbergite, titanaugite, omphacite spodumene and jadeite.
		Titanaugite, found in alkali-gabbos and alkali olivine basalts, has a high titanium content and is violet and purple-brown.
		Omphacite is an unusually bright green mineral found in ecogites.
	www.quartznall.co.uk /learnclinopyroxene.htm (253 words)

	Practical Aspects of Thermobarometry
		The original file had a bulk composition formulation that differed from the proportions used to calculate gammas: this is no longer permitted.
		The formulae for proportions are a little difficult to visualise, because although the ordered omphacite is still defined only in terms of di and jd, the model must also be able to reproduce bulk compositions and activities for highly ordered Fe-rich pyroxenes near hed50:jd50.
		The resulting a-X relationships in the di-hed-jd-ac tetrahedron imply a transition from ordered to disordered pyroxene at about 25% acmite in omphacite at T = 500-550°C, in reasonable agreement with natural data from Oman and elsewhere.
	www.earth.ox.ac.uk /~davewa/pt/axcode_omp.html (375 words)

	EarthRef.org Reference Database (ERR) -- Yoder & Tilley 1962
		In the region of magma generation (below 60 km) the parental material, presumed to be garnet peridotite, yields an eclogitic magma and its fractionation depends on the garnet and omphacite of the eclogite, not on plagioclase and clinopyroxene of a basaltic magma.
		Increase of the garnet constituents in the magma at high pressure by effective removal of omphacite or shift of the garnet-omphacite boundary 'surface' will give rise to a tholeiite-type magma at low pressure.
		Similarly, increase of the omphacite constituents in the magma at high pressure by physical or physicochemical means will give rise to an alkali basalt-type magma at low pressure.
	earthref.org /cgi-bin/err.cgi?n=2603 (268 words)

	Globeinvestor.com: New Results From Dios' Chibouki Diamond Project
		So far, 351 heavy mineral samples were collected (25 still being processed) on the Mistissini claim block and another 60 on the Sauvage Lake block.
		The presence of eclogitic omphacite in specific samples appears to differentiate these trains from the one observed further north (G9-ILM File-Axe Lake train).
		Eclogite is a diamond source rock rarer than harzburgite, but a lot richer in diamonds.
	www.globeinvestor.com /servlet/ArticleNews/print/CCNM/20060119/0119127n (598 words)

	Mossbauer spectroscopy of omphacite and garnet pairs from eclogites: Application to
		The results show very low Fe /EFe ratios of 0.026 to 0.082 in garnet but high Fe /EFe ratios of 0.240 to 0.689 in omphacite.
		These maximum values provide close proxies to peak metamorphic temperatures provided that the retrograde exchange of Fe-Mg cations by diffusion between minerals during exhumation is taken into account.
		Mössbauer spectroscopy of omphacite and garnet pairs from eclogites: Application to geothermobarometry.
	www.uga.edu /~srel/Reprint/2844.htm (290 words)

	Relict coesite exsolution in omphacite from Western Tianshan eclogites, China -- Zhang et al. 90 (1): 181 -- American ...
		Relict coesite exsolution in omphacite from Western Tianshan eclogites, China -- Zhang et al.
		Relict coesite exsolution in omphacite from Western Tianshan eclogites, China
		for coesite, in addition to those of quartz and the host omphacite.
	ammin.geoscienceworld.org /cgi/content/abstract/90/1/181 (212 words)

	Plastic Deformation and Development of Clinopyroxene Lattice Preferred Orientations in Eclogites (ResearchIndex)
		Abstract: We use an anisotropic viscoplastic self-consistent (VPSC) model to simulate the development of omphacite lattice preferred orientations (LPOs) in response to deformation by dislocation glide.
		In these simulations, we consider slip systems identified either in naturally deformed omphacite or in experimentally deformed diopside.
		Simulated LPOs reproduce very well the characteristic omphacite LPO pattern in naturally deformed eclogites: a strong concentration of [001]-axes sub-parallel to the...
	citeseer.ist.psu.edu /bascou02plastic.html (215 words)

	Omphacite: Omphacite mineral information and data.
		There is no specific data on health dangers or toxicity for this mineral, however you should always treat mineral samples as potentially toxic/dangerous and use sensible precautions when handling them.
		Clark, Joan R. Papike (1969), Cation distribution in the crystal structure of omphacite, the eclogitic pyroxene: Geological Society of America Abstract for 1968.
		Champness, P.E. (1973), Speculation on an order-disorder transformation in omphacite: American Mineralogist: 58: 540-542.
	www.mindat.org /min-2991.html (226 words)

	Abstact LXX, 2002
		Since about 400°C, omphacite compositions become stable, and the miscibility gap still exists between omphacite and omphacite-rich jadeite, and reduces for increasing aegirine contents.
		For temperatures exceeding 450°C, compositional gaps between jadeite and omphacite are recorded.
		A compositional gap between omphacite and calcic pyroxene is likely, and tends to reduce for T > 700°C. * Corresponding author
	tetide.geo.uniroma1.it /riviste/permin/abstract02-1.htm (1416 words)

	Articles - Pyroxene (Site not responding. Last check: 2007-10-24)
		Sodium pyroxenes with more than 20 mol.% calcium, magnesium or iron(II) components are known as omphacite and aegirine-augite, with 80% or more of these components the pyroxene falls in the quadrilateral shown in figure 1.
		Table 1 shows the wide range of other cations that can be accommodated in the pyroxene structure, and indicates the sites that they occupy.
		Omphacite** (Calcium Sodium Magnesium Iron Aluminium Silicate)
	www.zdiamond.net /articles/Pyroxene (879 words)

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