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Topic: Phenocryst

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	Phenocryst Focus
		Phenocryst speaks from within your mind as well as conveys a sense of joy empathically.
		Phenocryst says in the form of thoughts, 'We must call to it.
		Phenocryst 's thoughts become your own, a feeling of joy overwhelms you, 'Because of you we can at last speak with our maker.
	p203.ezboard.com /fequanimityfrm2.showMessage?topicID=11.topic (2807 words)

	Tubular voids in labradorite
		In thin section, the phenocrysts of all types and sizes exhibit an array of shapes and textures, many of which resemble the skeletal forms typically developed among crystals that grew rapidly in response to conditions of supersaturation.
		In view of the large number of phenocrysts examined, their apparent absence cannot be wholly ascribed to the fortuitous orientation required, wherein the axis of a tube must lie in the plane of the section.
		Essential absence of the third dimension leaves doubt as to whether an elongate re-entrant in the margin of a phenocryst truly represents a tube in longitudinal section or merely the outline of a platy re-entrant of vesicular groundmass material that was cut by the section.
	www.minsocam.org /MSA/collectors_corner/arc/labradorite.htm (3576 words)

	Phenocryst (Site not responding. Last check: 2007-10-25)
		A phenocryst is a relatively large and usually conspicuous crystal formed in the mass of a porphyritic igneous rock.
		For example, olivine may form the primary phenocrysts of some materials, and as such is used to define the subtype of that material (e.g., an olivine felsite).
		Phenocrysts are commonly found in materials such as felsite and andesite.
	phenocryst.iqnaut.net (75 words)

	University of Windsor - Terence E Smith Web Site-Field descriptions and Phenocryst Chemistry (Site not responding. Last check: 2007-10-25)
		The andesites are characterized by mixtures of olivine, plagioclase, clinopyroxene, and orthopyroxene phenocrysts with microphenocrysts of opaque oxides.
		In the basalts and basaltic andesites the plagioclase phenocrysts occur as subhedral to euhedral tabular crystals.
		In the andesites the plagioclase phenocrysts occur as tabular, euhedral to subhedral crystals.
	www.uwindsor.ca /users/t/tsmith/main.nsf/9d019077a3c4f6768525698a00593654/c3910c3dba07a4e585256dc8005f42fb!OpenDocument (2664 words)

	Phenocryst - Wikipedia, the free encyclopedia
		A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock.
		For example, olivine may form the primary phenocrysts of some materials, and as such is used to define the subtype of that material (e.g., a 'porphyritic olivine basalt').
		The term phenocryst is used for a crystal that is significantly larger than the average size of the groundmass crystals; in practice, these are generally >~1 mm.
	en.wikipedia.org /wiki/Phenocryst (441 words)

	Pallister
		Comparison of mineral compositions and textures indicates that the olivine (Fo), clinopyroxene (Mg# 75-85), and many of the hornblende phenocrysts were derived from basaltic magma similar to the inclusions in the June 7-12 dome, whereas the plagioclase, cummingtonite, and anhydrite phenocrysts are from June-15 type dacitic magma.
		Olivine phenocrysts in the hybrid andesite are rimmed by aggregates of hornblende laths (fig.
		Studies of melt and vapor inclusions in phenocrysts and phase equilibria (Westrich and Gerlach, 1992; Rutherford and Devine, this volume) indicate that the June 15 dacitic magma was saturated with a water-rich fluid phase prior to eruption.
	pubs.usgs.gov /pinatubo/pallister (15114 words)

	Will the Real Phenocryst Please Stand Up? III Posters - Volcanology, Geochemistry, Petrology [V]
		Xenocrysts of olivine, anorthite and Mg-rich augite are derived from the disaggregation of mafic xenoliths.
		Phenocrysts of samples collected from the 1939-1941 dacite lava flows were analyzed for major and trace element compositions using the EMP and SIMS, with particular focus on concentrations of Li, Be and B. Three types of plagioclase phenocrysts are highlighted in this study.
		The phenocryst assemblage of the lava, and the mineral assemblage of the crystal clots, is: plagioclase, hornblende, orthopyroxene, clinopyroxene, olivine and oxide minerals.
	www.agu.org /meetings/fm05/fm05-sessions/fm05_V13B.html (14456 words)

	World Decriptions (Site not responding. Last check: 2007-10-25)
		The phenocryst chamber is one of the most intact and maintained in all of Strata (seconded only by the one in TLA), but unfortunately with no source of Erredy Powder.
		The incoming and departing phenocryst chambers are surprisingly intact, with the former including a sign saying "Welcome to Asthenia." On the same island as the incoming phenocryst chamber, there is an abandoned hut carved into the rock wall and several different forms of stationary battle machines.
		The phenocryst is sealed, and opening it involves directing a beam of light across a nearby console.
	www25.brinkster.com /akril/Torin/Worlds.html (1693 words)

	ANALYSIS OF PHENOCRYST TEXTURES AND SIZE DISTRIBUTION, CARLTON RHYOLITE, WICHITA MOUNTAINS, SOUTHWESTERN OKLAHOMA
		Phenocrysts of Qtz (50-65%) and Ksp (35-50%) are set in a fine-grained granular matrix of Qtz and Ksp.
		Qtz phenocrysts in the upper section of the formation exhibit extensive brittle fracturing, whereas within Ksp phenocrysts fractures may diffuse to a braided pattern and reconnect with fractures in the matrix on the other side of the crystal, rather than forming a single transgranular fracture.
		The fractured nature of the phenocrysts is consistent with deformation during a later tectonic event, rather than during emplacement and suggests deposition as a flow, rather than as an explosive pyroclastic airfall.
	gsa.confex.com /gsa/2006SC/finalprogram/abstract_100027.htm (515 words)

	Planet Earth I: Igneous Rocks
		Phenocrysts of olivine is diagnostic of a basic composition.
		They commonly have phenocrysts of quartz and feldspar, with minor hornblende and mica, but there are usually not sufficient phenocrysts for the rock to be termed porphyritic.
		Olivine is the most commonly seen phenocryst, being a high temperature, early crystallising mineral, but light, rectangular plagioclase and fl pyroxene may also be seen in phaneritic samples.
	www.rpi.edu /dept/geo/pe1/chapter6.html (7841 words)

	Will the Real Phenocryst Please Stand Up? I - Volcanology, Geochemistry, Petrology [V]
		Numerous mafic (basalt to basaltic andesite) lavas from volcanic arcs throughout the world contain large (2 to 10 mm diameter) augite phenocrysts that are commonly sector zoned and invariably concentrically zoned, where the concentric zoning consists of zones of optically clear augite separated by thin zones rich in mineral and melt inclusions.
		Phenocryst zoning in plagioclase, hornblende and apatite is diverse, with oscillatory, simple, multiple and patchy zoning and sieve textures identified.
		Phenocryst proportions in many mafic lavas of the Quaternary Tatara-San Pedro complex (TSPC; 36°S, Chilean Andes) are minor compared to modal abundances of coarse olivine, clinopyroxene, and plagioclase xenocrysts derived from disaggregated mafic-Ultramafic xenoliths.
	www.agu.org /meetings/fm05/fm05-sessions/fm05_V11A.html (2709 words)

	TEXTURES REFERRING TO OVERGROWTH (Site not responding. Last check: 2007-10-25)
		Where the overgrowth forms a more or less continuous rim around the enclosed mineral, such as, for example, the rim of plagioclase around a proportion of orthoclase phenocrysts in some textural varieties of rapakivi granite, it may be termed a mantle.
		A conspicuous example is the occurrence of prominent “fl rims” composed of small granules of pyroxene and opaque oxide mineral around hornblende and biotite phenocrysts in andesite and latite flows.
		Oscillatory zoning is often evident in the plagioclase phenocrysts of andesite, originating intratellurically in high level magma chambers where a complex crystallization history is inferred.
	www.metu.edu.tr /home/www64/geoweb/igneous-overgrowth.htm (753 words)

	WHOI : People : Alison Shaw : Publications
		We report new He abundance and isotope measurements of phenocryst phases in volcanic tephra and lavas from the Nicaragua-Costa Rica section of the Central American arc, where significant variations in crustal thickness have been inferred. Helium isotope values range from 4.2 R
		He ratios measured in phenocryst phases show good agreement with He isotope values of geothermal fluids from the same volcanoes.
		He ratios in pyroxenes is related to the closure temperatures of the phenocryst phases. Given its lower closure temperatures and higher He diffusion rates, we suggest that pyroxenes would be more susceptible to late-stage He exchange with a low
	www.whoi.edu /hpb/viewPage.do?id=4618&cl=1 (259 words)

	::: JAPAN EXPEDITION : TOOLS AND TECHNIQUES : LAVA CHEMISTRY :::
		We are not only interested in the bulk rock geochemistry, but in crystals called phenocrysts and the bits of magma trapped in them as well.
		Pieces of the rocks that were not powdered are gently crushed, and phenocrysts such as olivine, pyroxene, and plagioclase are separated out.
		Because melt inclusions can be analyzed using both the mass spectrometer for major and trace elements and the ion probe for volatiles, they are powerful tools for understanding magma generation beneath arcs, since they potentially trap the composition of the earliest melt.
	sio.ucsd.edu /japan/equipment/lava.cfm (279 words)

	Title page for ETD etd-08192002-150340 (Site not responding. Last check: 2007-10-25)
		Silicate melt inclusions are ubiquitous in quartz phenocrysts, yet there are few studies of such inclusions from porphyry copper systems.
		If a phenocryst is able to preserve the original parent magma, then accurate information can be obtained for ancient volcanic systems.
		Melt inclusions are difficult to recognize in quartz phenocrysts from porphyry copper system because they are crystalline and hidden by exsolved magmatic volatiles.
	scholar.lib.vt.edu /theses/available/etd-08192002-150340 (482 words)

	David
		Abundant broken crystal fragments in the groundmass of the phenocryst-poor groundmass and preservation of the same phenocryst assemblage in the two pumice types favor the second explanation.
		Alternatively, extreme volatile concentration at the top of the reservoir could have inhibited phenocryst development, and thus the earliest tapped magma (from the top of the reservoir) would have produced a relatively high percentage of phenocryst-poor pumice.
		However, this hypothesis is not consistent with the presence of the same phenocryst mineral assemblage in both types, including late-grown cummingtonite, which indicates that both pumice types had initially crystallized to the same extent, nor does it explain the fragmental textures in the phenocryst-poor pumice.
	pubs.usgs.gov /pinatubo/david (1829 words)

	Will the Real Phenocryst Please Stand Up? II - Volcanology, Geochemistry, Petrology [V]
		However, recent study of individual "phenocrysts" and their size fractions for oxygen isotope composition by laser fluorination, and core and rim study by SIMS, reveal isotope zoning and intracristalline variability, which exceeds analytical uncertainty, and often reach several permil.
		Phenocryst Dynamics in the Magma Chamber of the Guadeloupe Soufriere From U-Th-Ra Disequilibria in 1440A.D. Lavas
		We augment this well-constrained case study with new in situ Sr isotope analyses for one of the Soufriere lavas and a cumulate xenolith erupted in 1979.
	www.agu.org /meetings/fm05/fm05-sessions/fm05_V12A.html (3057 words)

	Volcanic and Geologic Terms
		Phenocryst: A conspicuous, usually large, crystal embedded in porphyritic igneous rock.
		Shoshonite: A trachyandesite composed of olivine and augite phenocrysts in a groundmass of labradorite with alkali feldspar rims, olivine, augite, a small amount of leucite, and some dark-colored glass.
		Xenocrysts: A crystal that resembles a phenocryst in igneous rock, but is a foreign to the body of rock in which it occurs.
	volcano.und.nodak.edu /vwdocs/glossary.html (4560 words)

	[No title] (Site not responding. Last check: 2007-10-25)
		Cumulus minerals (pl, opx, cpx, hb, ol, ox) are the same phases that occur as phenocrysts in MSH volcanic rocks, although mineral compositions from the xenoliths show wider ranges in compositions.
		The lack of a 1:1 correspondence between most cumulus and phenocryst assemblages suggests that as new batches of magma made their way through the overlying pluton they incorporated fragments from the still-hot crystal residue of previous magmatic episodes.
		This model is consistent with geophysical data from MSH and the surrounding area, which indicates that a ductile zone at depths of 7-11 km, of which only the central zone is molten.
	zephyr.rice.edu /sota/papers/Pallister,JohnPallisterSOTA.doc (666 words)

	Global Volcanism Program \| Taftan \| Monthly Reports (Site not responding. Last check: 2007-10-25)
		Plagioclase is the predominant phenocryst phase (30-40%) with hornblende (< 5%), pyroxene (< 1%), opaque Fe-Ti oxide phases (< 1%), and trace amounts of biotite.
		The phenocryst assemblage of the lava sample suggests multiple phenocryst sources and disequilibrium between mineral phases and groundmass, typical of stratovolcanoes.
		The correspondence of some phenocryst phases with mineral phases in microxenoliths suggest that at least some of the phenocrysts were inherited during the assimilation of country rock, while the oscillatory zoning, sieve-textured cores and mantles, and multiple dissolution surfaces in feldspars indicates that other phenocrysts have undergone long and complex magmatic histories.
	www.volcano.si.edu /world/volcano.cfm?vnum=0302-05-&volpage=var (1149 words)

	IGNEOUS PETROLOGY AND VOLCANOLOGY3
		Porphyritic rocks were named by phenocryst type, where the term "phenocryst" was used for a crystal that was significantly (typically five times) larger than the average size of the groundmass crystals and/or generally euhedral in shape.
		Phenocryst abundance descriptors were further modified by including the names of phenocryst phases, in order of decreasing abundance.
		The percentages of individual phenocryst, groundmass, and alteration phases were estimated visually, and textural descriptions were reported (see "Site 1173 Thin Sections").
	www-odp.tamu.edu /publications/196_IR/chap_02/c2_8.htm (2098 words)

	TEXTURES REFERRING TO THE GRANULARITY OF (Site not responding. Last check: 2007-10-25)
		Thus an equigranular granite, for example, devoid of phenocrysts would not be termed aphyric.
		There are number of larger grains called phenocrysts, surrounded by a population of grains of significantly smaller size, the groundmass.
		in the figure, both the phenocrysts and the groundmass are fine grained (aphanitic).
	www.metu.edu.tr /home/www64/geoweb/igneous-granularity.htm (465 words)

	AGE DETERMINATIONS
		Ar age determinations were performed on plagioclase, sanidine, amphibole, and biotite phenocrysts from volcanic rocks covering the spectrum from basalt to rhyolite.
		A single sanidine phenocryst yields the most precise age estimate for the eruption of rhyolite 7521.
		Ar analyses of plagioclase, sanidine, biotite, and amphibole phenocrysts from lava clasts in Cores 161-977A-60X-63X and 978A-47R indicate that the eruptions of these basaltic to rhyolitic magmas occurred between 6.1 (dacite 7525) and 12.1 Ma (dacite 7524).
	www-odp.tamu.edu /publications/161_SR/chap_27/c27_5.htm (697 words)

	[No title]
		This is especially true for Legs 103 and 104 where the paper form was designed to collect primary and secondary mineralogy data only.
		In the data file, if primary mineralogy was reported (rather than phenocrysts and groundmass), it is stored in the groundmass data items with the phenocrysts data items left blank.
		The core is subdivided into lithologic units, using the criteria of changing grain size, occurrence of glassy margins, and changes in petrographic type and phenocryst abundances.
	www.ngdc.noaa.gov /mgg/geology/odp/docs/hrthin.txt (850 words)

	Magmagenesis at Soufriere Volcano, St Vincent, Lesser Antilles Arc (Site not responding. Last check: 2007-10-25)
		Roobol and Smith, (1975) recorded a progressive change from early erupted basaltic andesite to late basalt in the 1902-1903 activity, perhaps pointing to the existence of zoned magma chambers at least spasmodically beneath Soufriere.
		Melt (glass) inclusions occur in all the phenocryst phases (Graham and Thirlwall, 1981; Devine and Sigurdsson, 1983; Bardintzeff, 1992).
		The majority of clinopyroxene phenocrysts are augite, although diopsidic cores are found in olivines and augites in more magnesian rocks, e.g.
	library.iem.ac.ru /j-petr/10-3998/html/egb066_gml.html (3267 words)

	Glenn A. Gaetani MS thesis abstract (Site not responding. Last check: 2007-10-25)
		In contrast with most other MORB suites, plagioclase is a major phenocryst phase in only one sample and is absent completely from 38.5% of the thin sections.
		Although the appearance and disappearance of phenocryst phases agrees very well with the phase equilibria in the system An-Fo-Di, no simple relationship exists between the Mg/(Mg + Fe) ratio of the liquid and the phenocryst assemblage.
		The problem of needing to crystallize significant amounts of clinopyroxene to explain a suite of MORB which does not contain clinpyroxene is not unique to this study, but has been recognized by other workers for a number of years.
	www.albany.edu /geosciences/gaetania.html (624 words)

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