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Topic: Plagioclase

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	plagioclase.htm
		- Plagioclase is abundant in the Marinette Quartz Diorite with quartz and biotite.
		Plagioclase is abundant in the Marinette Quartz Diorite with quartz, hornblende and biotite.
		Plagioclase is abundant in the Newington Tonalite, exposed on Highway 8 in the NW sec.
	www.uwrf.edu /~wc01/plagioclase.htm (1626 words)

	Plagioclase - Wikipedia, the free encyclopedia
		Plagioclase feldspars are a very, very important group of igneous rock forming tectosilicate minerals.
		Plagioclase feldspars range between two endmembers: the sodic feldspar endmember albite and the calcic feldspar endmember anorthite.
		The members of this series are known as the sodic-lime feldspars, and as a group are called the plagioclase feldspars, which comes from Greek meaning "oblique fracture" in reference to the two not-quite-right-angle cleavages.
	en.wikipedia.org /wiki/Plagioclase (461 words)

	PLAGIOCLASE - LoveToKnow Article on PLAGIOCLASE (Site not responding. Last check: 2007-10-06)
		The mean indices of refraction and the angles of extinction on the cleavages P and M are given in the accompanying table.
		A detailed summary of the optical characters and their employment in discriminating the several members of the plagioclase series is given by H. Rosenbuch, Mikroskopische Physiographie der Mineralien und Gesteine (4th ed.
		The plagioclases occur as primary constituents of igneous rocks of almost every kind, and are also frequent as secondary minerals in metamorphic rocks.
	11.1911encyclopedia.org /P/PL/PLAGIOCLASE.htm (755 words)

	Skaergaard intrusion photomicrographs (Site not responding. Last check: 2007-10-06)
		Cumulate phases are plagioclase, olivine, augite, ferrobustamite(?), oxides, and apatite.
		Mineralogy: plagioclase, augite, olivine (mostly altered to a mass of serpentine, talc, and magnetite), oxides, apatite.
		The plagioclase porphyry dike that is one of the oldest in the Skaergard Homestead area, based on crosscutting relationships.
	www.union.edu /PUBLIC/GEODEPT/hollocher/skaergaard/geologic_features/micrographs.htm (2034 words)

	Plagioclase
		Plagioclase (a feldspar) is widespread and common in a wide variety of igneous and metamorphic rocks and, to a much lesser extent, in some immature sedimentary rocks.
		Plagioclase may be confused with quartz, but quartz lacks cleavage, lacks twinning, does not alter, exhibits undulatory extinction, and is uniaxial.
		In plagioclase, the contacts between twins tend to be sharp, while in microcline they are not.
	www.und.nodak.edu /instruct/mineral/320petrology/opticalmin/plagioclase.htm (971 words)

	GEOCHEMICAL EFFECTS OF RECRYSTALLIZATION AND EXSOLUTION OF PLAGIOCLASE OF FERROAN ANORTHOSITE (Site not responding. Last check: 2007-10-06)
		The minor- and trace-element composition of plagioclase of ferroan anorthosite is of special significance because it is used to infer the composition and the geochemical and petrologic evolution of the magma from which it crystallized.
		We attribute the clouding to exsolution and clear regions of plagioclase to loss of exsolved components; clear recrystallized areas indicate that recrystallization took place under conditions in which the mafic components were less soluble in plagioclase than they were during primary crystallization.
		In clouded plagioclase, the mafic components are therefore part of the primary plagioclase and should be considered (as in bulk analyses) in estimates of equilibrium melt compositions.
	www.gps.caltech.edu /users/whsu/pub/LPSC27_2.html (1327 words)

	PLAGIOCLASE FELDSPAR (Site not responding. Last check: 2007-10-06)
		Plagioclase feldspars are one of the most important components of almost ALL igneous and metamorphic rocks.
		Most calcium-rich plagioclase feldspars are very unstable at the earth’s surface and rapidly break down into a soft mush of clay minerals, with calcium and sodium ions that are washed away in solution.
		Plagioclase feldspars are used as a component of mixtures that are melted to form ceramics and glasses for industrial use (as electrical insulators and pottery glazes).
	www.brookes.ac.uk /geology/sedmins/plagiocl.html (579 words)

	METAMORPHIC PETROLOGY
		Coronitic replacement of olivine and plagioclase by talc, chlorite, and tremolite characterizes the alteration of troctolitic rocks in the interval from 28.2 to 34.1 mbsf.
		Plagioclase is slightly altered (5%–10%) to secondary plagioclase and minor chlorite.
		Plagioclase relics are variably affected by a late-stage low-temperature overprint, resulting in the formation of clay and carbonate (Fig.
	www-odp.tamu.edu /publications/209_IR/chap_10/c10_3.htm (3469 words)

	Exsolution
		Plagioclase feldspars exsolve to form albite, a Na-rich feldspar and anorthite, a Ca-rich plagioclase.
		The initial composition of the mixed plagioclase was 47 to 58% molecular anorthite and 42 to 53% albite.
		Huttenlocher intergrowths occur when the initial composition of the plagioclase was 60 to 85% molecular anorthite and 14 to 40% albite.
	www.utexas.edu /tmm/npl/mineralogy/Science_of_Minerals/Exsolution.htm (420 words)

	[No title]
		Plagioclase Clinopyroxene Olivine Orthopyroxene 55 39 5 1 1-10 mm.
		Plagioclase Pyroxene Olivine 60 40 8 0.1-5 mm.
		Plagioclase Clinopyroxene Olivine 52 40 8 2-5 mm.
	www.ngdc.noaa.gov /mgg/geology/odp/data/118/735B/charvi.dat (823 words)

	The significance of plagioclase-dominant coronas on garnet, Wenatchee Block, northern Cascades, Washington, U.S.A.
		Plagioclase in all samples is mostly anhedral and unzoned, but many grains include small An cores with oscillatory zoning that are interpreted as relict phenocrysts.
		Plagioclase composition and texture, and phase-equilibria constraints on mineral reactions, are most compatible with garnet growth by replacement of igneous high-An plagioclase plus chlorite by "new" lower-Ca (An) plagioclase and garnet.
		Incomplete progress of the reaction, as indicated by persistence of coronas and "relics" of primary plagioclase, may be due to an abrupt decrease in temperature, with possible loss of fluid.
	pubs.nrc-cnrc.gc.ca /mineral/tcm-36743-1.html (713 words)

	Serpentinite (Site not responding. Last check: 2007-10-06)
		Plagioclase is a framework silicate in the feldspar group.
		Plagioclase is generally white with two distinctive cleavage planes at nearly right angles.
		Plagioclase can sometimes be distinguished from potassium feldspar by the presence of twinning which is visible as fine striations on the crystal faces.
	pangea.stanford.edu /~mary/geo116/minerals/plagioclase.html (53 words)

	Plagioclase Feldspar Data (Site not responding. Last check: 2007-10-06)
		Plagioclase is an alkalai feldspar that is one of several feldspar minerals, including sanidine, orthoclase, and microcline.
		There are several types of plagioclase feldspar which differ from one another based on variations in relative calcium and sodium content, including albite, oligoclase, andesine, labradorite, bytownite and a northite.
		Plagioclase is the most common feldspar, and occurs in igneous, metamorphic, and as (uncommon) detrital grains in sedimentary rocks.
	www.uwm.edu /Course/422-100/Mineral_Rocks/plagioclase.feldspar.data.html (199 words)

	USGS Geology in the Parks
		Plagioclase is a member of the feldspar mineral family.
		Plagioclase feldspars are yet another silicate that contains considerable sodium or calcium.
		Like plagioclase feldspar, potassium feldspars are silicate minerals that contain a considerable amount of -you guessed it- potassium.
	wrgis.wr.usgs.gov /docs/parks/rxmin/mineral.html (338 words)

	Lab 7: Intermediate and silicic igneous rocks; determining plagioclase compositions
		Plagioclase is perhaps the most abundant of the rock-forming minerals commonly seen in thin section.
		Compositions of plagioclase are usually expressed in terms of the percentage of the anorthite molecule in the plagioclase (e.g.
		Note that parallel extinction for plagioclases occurs in the middle of the compositional range of oligoclase.
	www.eos.ubc.ca /courses/eosc221/labs/lab7.html (421 words)

	Mineral Description (Site not responding. Last check: 2007-10-06)
		Colourless plagioclase grains, note cleavage to right of label, surrounded by a large oikocryst of clinopyroxene
		Plagioclase also may alter to saussurite, a fine grained aggregrate of epidote group minerals, albite, sericite and other minerals.
		The composition of igneous plagioclase will reflect the composition of the melt from which the mineral formed.
	www.brocku.ca /earthsciences/people/gfinn/minerals/plag.htm (246 words)

	Feldspar : Plagioclase (Site not responding. Last check: 2007-10-06)
		This group of minerals consists of three silicates: a potassium-aluminium silicate (the orthoclase feldspars), a sodium-aluminium silicate, and a calcium-aluminium silicate (the plagioclase feldspars) and their isomorphous mixtures.
		The members of this series are known as the soda-lime (or lime-soda) feldspars, and as a group are called the plagioclase feldspars (from the Greek meaning "oblique fracture," in reference to the two not-quite-right-angle cleavages).
		The intermediate members of the plagioclase group are very similar to each other and cannot be distinguished except by optical means.
	www.findword.org /pl/plagioclase.html (947 words)

	Search Results for plagioclase - Encyclopædia Britannica
		Plagioclase is a mixture of albite (Ab), or sodium...
		a feldspar mineral in the plagioclase (q.v.) series that is often valued as a gemstone and as ornamental material for its red, blue, or green iridescence.
		Type of feldspar mineral in the plagioclase series that is often...
	www.britannica.com /search?query=plagioclase&submit=Find&source=MWTEXT (322 words)

	[No title] (Site not responding. Last check: 2007-10-06)
		All are characterized by plagioclase laths that project inward from the rims of the chondrules, to varying lengths into the interiors.
		Plagioclase ranges in composition from An~60 to An~100; in some chondrules the larger individual crystals show optical zonation.
		The textures and mineral chemistry indicate unambiguously that the plagioclase is not only a primary igneous phase in these chondrules, but is the liquidus phase as well.
	www.gps.caltech.edu /~whsu/pub/Wash95_2.html (564 words)

	Plagioclase
		Plagioclase feldspars show a complete compositional variation between sodium-rich plagioclase, albite, and calcium-rich plagioclase, anorthite.
		Plagioclase is an important rock-forming mineral and occurs widely, primarily in igneous rocks such as basalts.
		It can sometimes be confused with alkali feldspars (such as orthoclase) but can be distinguished by striations on the cleavage surfaces caused by the intersection of lamellar twins with the cleavage surface.
	www.es.ucl.ac.uk /schools/Glossary/plagioclase.htm (117 words)

	Plagioclase (Site not responding. Last check: 2007-10-06)
		Housh and Luhr (1991, 1994) presented a model for plagioclase - melt equilibria in silicate melts.
		The equilibria between the albite and anorthite components in a melt and coexisting plagioclase were calibrated over a range of pressures, temperatures, and water contents in equations 5 and 6.
		Variations in water content have a profound effect on plagioclase composition for a given pressure, temperature, and melt composition.
	www.geo.utexas.edu /isochem/plag_melt.htm (444 words)

	MYRMEKITE 43 of 50
		K in the mixed Na-K plagioclase feldspar allows this feldspar (hosting the quartz blebs) to fade into the microcline as the K-content in the altered lattice gradually increases to the amounts in the adjacent microcline.
		Note that the albite twinning of the plagioclase in the wartlike myrmekite is optically continuous with the albite twinning in the non quartz bearing, recrystallized plagioclase crystal outside the microcline (Fig.
		As these microfractured plagioclase crystals were replaced in their interiors by microcline and grew in size, subsequent microfracturing occurred in zoned plagioclase crystals only adjacent to the border of the growing microcline crystal but not beyond the border into the other groundmass zoned plagioclase crystals.
	www.csun.edu /~vcgeo005/Temecula.htm (4651 words)

	Structural Petrology of Plagioclase Peridotites in the West Othris Mountains (Greece): Melt Impregnation in Mantle ...
		Structural Petrology of Plagioclase Peridotites in the West Othris Mountains (Greece): Melt Impregnation in Mantle Lithosphere -- DIJKSTRA et al.
		Structural Petrology of Plagioclase Peridotites in the West Othris Mountains (Greece): Melt Impregnation in Mantle Lithosphere
		plagioclase and clinopyroxene as cumulate phases and refertilizing
	petrology.oupjournals.org /cgi/content/abstract/42/1/5 (268 words)

	Practical Thermobarometry Part 2: Mineral Groups - plagioclase
		Metamorphic plagioclases generally contain very limited K, although in the granulite facies truly ternary Na-Ca-K feldspars may be encountered.
		In metamorphic plagioclases it is usually possible to ignore the minor substitution of K, and to assume that all sites are filled.
		The zonation is commonly arranged concentrically in plagioclase grains.
	www.earth.ox.ac.uk /~davewa/pt/pt02_pl.html (379 words)

	MYRMEKITE 21 OF 50
		On close examination of the thin sections of the augen gneiss at outcrop ONE, the rims of the zoned augen consist of sericitized plagioclase grains and sericitized myrmekite whose quartz vermicules are the same size as in myrmekite bordering zoned K-feldspar crystals in outcrop THREE (Fig.
		That is, there is no evidence for the migration of felsic materials from the plagioclase amphibolite that would produce a greater concentration of mafic components as a residue in the plagioclase amphibolite immediately adjacent to the supposed expelled felsic components in the granitic masses.
		lThe absence of orthopyroxene in the plagioclase amphibolite and local abundance of primary biotite suggest that the quartz sieve textures in the biotite are the result of replacement of biotite by quartz rather than the reaction of K-bearing fluids with orthopyroxene to produce biotite and left-over quartz.
	www.csun.edu /~vcgeo005/three.htm (2529 words)

	Petrogenesis of plagioclase phenocrysts of Mount Etna, Sicily, with particular reference to the 1983 eruption; ...
		Petrogenesis of plagioclase phenocrysts of Mount Etna, Sicily, with particular reference to the 1983 eruption; contribution from catholdoluminescence petrography -- Stirling et al.
		The cathodoluminescence (CL) characteristics of plagioclase phenocrysts in water-quenched lavas from the 1983 eruption of Etna have been investigated to examine the application of plagioclase CL to the study of magmatic processes.
		The phenocrysts have a green luminescent inner zone that is sharply bounded by a blue luminescent outer zone, with the boundary often coinciding with a concentric zone of glass inclusions.
	minmag.geoscienceworld.org /cgi/content/abstract/63/2/189 (227 words)

	PLAGIOCLASE FLOTATION CUMULATE IN FERROBASALTS OF THE WESTERN SNAKE RIVER PLAIN: IMPLICATIONS FOR EVOLUTION OF ...
		Lava flows with flotation cumulates comprise three zones: a central, plagioclase porphyry with intersertal to intergranular textures in the groundmass, an upper diktytaxitic zone comprising plagioclase laths with large voids and minor intergranular mafics and glass, and a lower aphyric zone of ferrobasalt, with 16-17% FeO*.
		Plagioclase flotation cumulates beneath this ferrobasalts ceiling display a horizontal contact between the diktytaxitic and plagioclase porphyry zones; we interpret this horizon to represent the contact between interstitial melt (below) and volcanic gasses (above), and suggest that interstitial melt was displaced by the rising gasses.
		Plagioclase phenocrysts are An65 in both the porphyry and diktytaxitic zones, suggesting formation the plagioclase framework by simultaneous crystallization throughout the flow, followed by sinking of the dense, interstitial ferrobasaltic liquid to the bottom of the flow.
	gsa.confex.com /gsa/2004RM/finalprogram/abstract_72581.htm (517 words)

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