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Topic: Euhedral


In the News (Sun 13 Apr 14)

  
  Euhedral Commands
Once the EUHEDRAL command filter had been used and the subfile.hkl is present, it is not necessary to run readhkl at every program start.
This information is used for the determination of the redundancy in the filter routine, and for the calculation of R values.
All EUHEDRAL refinements of the crystal shape are based on this R2.
www.crystal.chem.uu.nl /distr/euhedral/commands.html   (2471 words)

  
  Euhedral - Wikipedia, the free encyclopedia
Euhedral refers to well-formed crystals with sharp, easily-recognized faces.
In rocks, the presence of euhedral crystals may signify that they formed early in the crystallization of a magma or perhaps crystallized in a cavity or vug, without hindrance from other crystals.
Etymology: Euhedral is derived from the Greek hedron meaning shape.
en.wikipedia.org /wiki/Euhedral   (219 words)

  
 gold from Appalachians
Euhedral gold crystals are extremely rare compared with the amount of the metal produced, and very few have been preserved.
Euhedral crystals and filiform gold develop in open spaces, for gold is too soft and malleable to displace most other minerals.
Therefore, it is rather remarkable that euhedral crystals of gold have not been reported previously from this region, but the writer has found no reference to such crystals in the literature.
www.minsocam.org /MSA/collectors_corner/arc/gold.htm   (2292 words)

  
 PYRITE Chapter 21. Sulfides, arsenides, antimonides, and sulfosalts
Some euhedral crystals are metastable and may decompose on exposure; the process, with respect to local material, is a relatively sluggish one, sometimes taking a half-century or more in institutional collections.
Equant, sharp, euhedral pyrite crystals in the white calcite of the Franklin Marble from Franklin.
Equant, euhedral pyrite crystal in the white calcite of the Franklin Marble from Franklin.
franklin-sterlinghill.com /dunn/ch21/pyrite.stm   (506 words)

  
 Medinah Minerals, Inc. - Vancouver Petrographic 10.6.00 Report
Clinopyroxene phenocrysts have euhedral but ragged (corroded) outlines up to 2 mm in diameter and are mantled by pale olive green amphibole (?hornblende) in parallel position.
Euhedral to subhedral magnetite crystals are mainly <0.2 mm in size.
Pyrite, forming euhedral crystals up to several mm across in massive aggregates in the major vein, or millimeter-sized crystals in the wallrock, is rarely associated with or contains rounded inclusions of sphalerite up to 0.75 mm across.
www.medinah-minerals.com /reports/petrographic_11-6-00.html   (7362 words)

  
 MYRMEKITE 29 OF 50
This euhedralism has generally been interpreted to suggest a deep (high-pressure-temperature) origin for the rock (Zen and Hammarstrom, 1984).
However, because the zoned plagioclase crystals indicate a relatively shallow emplacement rather than deep emplacement, the euhedral epidote must have been formed near the surface.
Therefore, euhedralism of epidote cannot always be used as an indicator of high P-T conditions for a rock's formation.
www.csun.edu /~vcgeo005/greece.htm   (1248 words)

  
 The petrography of the wallrocks and open-void fluorite mineralization at Rogerley Mine, Stanhope, North Pennines.   (Site not responding. Last check: 2007-11-04)
A late, coarse-grained, unzoned, euhedral dolomite/ankerite forms rims to small voids that are infilled by coarse-grained quartz and late-stage calcite next to local dedolomitisation.
Locally, subhedral to euhedral fluorite and galena, both associated with coarse-grained quartz, are enclosed within the 'chert'.
Galena forms subhedral to euhedral crystals within silicified limestone or is intergrown with green fluorite.
www.rosiehardman.com /goodprovenance/rogpet.htm   (1052 words)

  
 [No title]
The rocks are composed of 0.04-3 mm clasts including: scoriaceous, fluidal, and blocky palagonitized and chloritized glass shards; euhedral, subhedral, and broken olivine, augite, and plagioclase; accretionary lapilli; sub-rounded to angular basalt fragments.
The preservation of delicate glass shards and euhedral crystals, and the lack of non-volcanic material, indicates that this is a primary pyroclastic deposit.
Crystal morphologies such as large, euhedral olivine and clusters of granular augite are also found in the overlying olivine-pyroxene phyric flows of the Milne Land Formation.
www.geology.ucdavis.edu /~heister/AGU2001(LEH)abstract.doc   (654 words)

  
 Mineral Identification tips
K-feldspar (sanidine, orthoclase, microcline) - sub to euhedral, white to pink, stubby grains with 2 cleavages at 90 degrees.
Plagioclase - sub to euhedral, white, elongate to stubby grains with 2 cleavages at 90 degrees.
Distinguish from K-feldspar by presence of striations (caused by albite twinning) on cleavage surfaces.
www.ac.wwu.edu /~debari/406/mineralid.html   (268 words)

  
 Sandstone Images
A close-up of the previous image (96 Kb) The concentrically banded grain on the lower side of the fracture is probably a silicified volcanic (agate-like structure?).
Note that the microfracture on the left side of the image that is perpendicular to the macrofracture cuts the euhedral quartz cement that is filling the fracture.
Gray-scale image showing a split grain with complexly-zoned euhedral cement on either fracture face growing into the fracture porosity.
uts.cc.utexas.edu /~rmr/CLweb/private.html   (481 words)

  
 SUBMARINE CARBONATE DIAGENESIS IN A FOSSIL METHANE-METABOLIZING COMMUNITY: CAMPANIAN COQUINOID LIMESTONE IN THE PIERRE ...
Dense lucinid bivalve assemblages and carbonate cements with stable carbon isotope signatures indicative of mineral precipitation in the presence of methane are characteristic of the lenses.
Coquinoid limestones comprise pelletal packstones and grainstones, mostly articulated lucinid shells, and fibrous botryoidal, anhedral blocky, euhedral blocky and lublinite-like cements.
Microprobe analyses indicate that pelletal carbonates and botryoidal and anhedral blocky cements are magnesium rich, whereas lublinite cements are iron and magnesium rich, and blocky euhedral cements are iron rich.
gsa.confex.com /gsa/2003AM/finalprogram/abstract_64309.htm   (331 words)

  
 The -hedrals: euhedral, subhedral, and anhedral - Let's Get It Right Rocks & Minerals - Find Articles   (Site not responding. Last check: 2007-11-04)
It is interesting to note that, to date, these terms are found virtually exclusively in the literature of geology and related sciences; they cannot be found in general dictionaries, no matter how exhaustive they may be.
Euhedral, subhedral, and anhedral are essentially petrographic or rock descriptive terms, meaning that they owe their origin to petrographers who wanted to be able to unambiguously describe rock textures in thin sections of rocks as they examined them under a microscope.
The former and the latter formed under identical conditions at about the same time, so the "ball" of adamite has just as much right to be considered "euhedral" as do the individual crystals, yet I am certain that no one would ever apply the term to botryoidal adamite.
www.findarticles.com /p/articles/mi_m0GDX/is_5_77/ai_90983553   (874 words)

  
 SME--VIRTUAL ATLAS OF OPAQUE AND ORE MINERALS
Euhedral pyrite (light yellow-white, top left) and subhedral tetrahedrite (green-grey, centre) are harder than bornite (brown, top) and stromeyerite (pink-grey to blue-grey, bottom right).
Euhedral to subhedral pyrite (light yellow-white, bottom left) is replaced by copper-silver sulphides and is associated with tetrahedrite (green-grey, centre top).
Altered euhedral tetrahedrite (light grey, left) is rimmed by chalcopyrite (yellow, centre).
www.smenet.org /opaque-ore/Plate35.htm   (396 words)

  
 Ores and Metals   (Site not responding. Last check: 2007-11-04)
Discrete, subhedral to euhedral, broadly zoned or unzoned arsenopyrite crystals are 20 - 200µm but mainly 40 -120µm in length.
Trace amounts occur as 5 -20mm diameter crystals in the cores of altered FeTi oxides or as 5 -30µm diameter, anhedral to euhedral crystals often enclosed in a thin chalcopyrite rim in arsenopyrite.
Large, euhedral pyrite crystals, up to 0.5mm in diameter, present in thin quartz veins/lensoidal segregations carry numerous inclusions and are gold-bearing.
www.rosiehardman.com /goodprovenance/oresandmetals.htm   (1222 words)

  
 TEXTURES REFERRING TO THE   (Site not responding. Last check: 2007-11-04)
This texture is typical of granitic rocks in many of which quartz and orthoclase tend to be anhedral and plagioclase and biotite are subhedral to euhedral.
refers to a texture in which, theoretically, all the component mineral grains are euhedral (a geometrical impossibility in a holocrystalline rock).
The term is commonly applied to the texture of lamprophyres, which are characteristically densely and conspicuously crowded with euhedral mafic phenocrysts.
www.metu.edu.tr /home/www64/geoweb/igneous-crystalshape.htm   (422 words)

  
 Untitled Document
Optically clear quartz occurs as elongate, pencil like, euhedral crystals with a length to width ratio of 6:1 or greater.
Euhedral milky quartz is the most abundant variety found.
These overgrowths are equant in habit, with the base of the amethyst overgrowth terminated and forming a reentrant with the euhedral stem.
www.users.muohio.edu /rakovajf/RIqtz.html   (548 words)

  
 The -hedrals: euhedral, subhedral, and anhedral - Let's Get It Right Rocks & Minerals - Find Articles   (Site not responding. Last check: 2007-11-04)
It is interesting to note that, to date, these terms are found virtually exclusively in the literature of geology and related sciences; they cannot be found in general dictionaries, no matter how exhaustive they may be.
Euhedral, subhedral, and anhedral are essentially petrographic or rock descriptive terms, meaning that they owe their origin to petrographers who wanted to be able to unambiguously describe rock textures in thin sections of rocks as they examined them under a microscope.
The former and the latter formed under identical conditions at about the same time, so the "ball" of adamite has just as much right to be considered "euhedral" as do the individual crystals, yet I am certain that no one would ever apply the term to botryoidal adamite.
findarticles.com /p/articles/mi_m0GDX/is_5_77/ai_90983553   (874 words)

  
 E PGM in chromitites (Syum-Keu, Outocumpu ultramafic complexes)
Euhedral grain of laurite (LR) with inclusion of irarsite (IRS: IrAsS) and kashinite (KSH: (Ir,Rh)
Aggregate euhedral grain of laurite (LR) with native iridium-osmium alloy (Ir,Os).
Aggregate of native Cu with euhedral laurite (LR).
www.natires.com /epgm_crt.htm   (1158 words)

  
 Formation rates of calc-silicate minerals deposited inside drillhole casing, Ngatamariki geothermal field, New Zealand
Scanning electron microscopy (with EDAX attachment) and X-ray diffractometry aided the petrographic examination, which confirmed the identity of the minerals and showed that the epidote present is an Fe-rich variety and that prehnite and wairakite are nearly stoichiometric.
Some crystals show pitting that may be due to either local dissolution or, more likely because of their angular shape, to impacts between crystals or with the liner as the ejecta discharged.
Note that quartz saturation of the fluid has been established since euhedral quartz crystals are a minor phase present in some ejected chips.
www.minsocam.org /msa/collectors_corner/arc/geothermal.htm   (2541 words)

  
 Rhyolite2
Alunite occurs commonly in sections of altered tuff in several of the modern trench cuts surrounding the main mining area and the southeastern prospect.
The mineral occurs as euhedral, pseudohexagonal plates of a light pink color.
Although this species tends to form euhedral crystals, it is difficult to obtain attractive specimens, due to the small size of the cavities in the matrix and the difficulty experienced in trying to split the matrix in a controlled manner.
www.geocities.com /yedlinite/Rhyolite2.htm   (823 words)

  
 Speleothem Microfabrics   (Site not responding. Last check: 2007-11-04)
Layer in middle has calcite crystals with euhedral terminations (large red arrows), whereas upper layer has less well developed terminations (green arrow) and lower layer is flat (blue arrows) with no visible crystal terminations.
Euhedral crystal terminations of middle layer are evident because a zone of very small calcite scalenohedra (small red arrows) formed on top of them.
This is an unusual microfabric, in that the boundary between one calcite layer and an overlying calcite layer is usual subtle, because the overlying calcite nucleates on the lattice of the underlying layer, and no new crystals form.
www.gly.uga.edu /railsback/speleoatlas/SAimage0212.html   (161 words)

  
 Reappraisal of Magmatic Origin for Euhedral Analcimes in Volcanic Rocks
Analcime occurs as euhedral trapezohedrons embedded in aphanitic -and in some cases truly vitric- groundmass of silica-deficient volcanic rocks such as basanites, tephrites, phonolites, lamprophyres and blairmorites.
These are: enclosure of euhedral crystals in aphanitic and sometimes glassy matrix, radial trains of inclusions of igneous microlites, and absence of alterations in the accompanying olivines and pyroxenes.
Petrographic criteria and high structural iron set forth by Pearce (1993) for magmatic analcime have been observed to hold in case of Iranian analcimes-bearing volcanics for which secondary origin is indisputable.
www.mapindia.org /2005/papers/Poster/251.htm   (2111 words)

  
 Case Studies - PTTC Rockies
Here, finely crystalline euhedral-to-subhedral dolomite replaces calcareous grains and matrix (pink), leaving remnants of limestone texture shown in view A. Replacive dolomite is darker, with more inclusion material, whereas pore-filling dolomite is euhedral, inclusion-poor, and exhibits ferroan rims (arrow) in places.
General view of dolomite texture shows well-packed, finely crystalline dolomite in matrix, with coarser, euhedral dolomite filling porosity at center.
This dark area is a patch of partially dissolved and replaced, microporous chert (note remnant chert at bottom right), that was likely similar in texture to silica patch shown in A. Textures shown here suggest that pore-filling dolomite precipitated after silica.
www.mines.edu /research/PTTC/casestudies/lecrr/plate8.html   (242 words)

  
 Euhedral sinhalite crystals from Sri Lanka Mineralogical Record - Find Articles
Crystal #2 (#133408) measures 11 x 7 x 5 mm, weighs 0.717 g and is completely euhedral.
As these are the only euhedral crystals of sinhalite known to us, save the one from Burma, a description and comparison with the British Museum crystal seem appropriate.
The gemstones of Sri Lanka are found in ancient alluvial deposits eroded from Precambrian rocks of the Highland and Southwest groups.
www.findarticles.com /p/articles/mi_qa3672/is_199503/ai_n8727649   (873 words)

  
 E PGMs in Outocumpu Ophiolites (Finland)
However, we shall mark, that replacement of anduoite by irarsite allows us to suppose that anduoite is synchronous to laurite, erlichmanite and sperrylite and, consequently, to formation of ultramafic complex itself.
Euhedral primary grain of laurite (LR) distinctly visible.
Inclusion of irarsite (IRS) in euhedral crystal of gersdorffite(GF).
www.natires.com /epgm_outo.htm   (1284 words)

  
 NMBGMR Circular 141   (Site not responding. Last check: 2007-11-04)
The camptonites have large phenocrysts of euhedral hornblendes and altered diopsidic augite with minor phenocrysts of plagioclase.
This study is concerned with the petrography and petrogenesis of the diorites and associated camptonites in the central Sacramento Mountains.
Mineralogically, both rocks consist of phenocrysts of diopsidic augite, euhedral green hornblende, and plagioclase in a groundmass of plagioclase laths, interstitial chlorite, minor orthoclase, magnetite, and apatite.
geoinfo.nmt.edu /publications/circulars/141/home.html   (548 words)

  
 Euhedral sinhalite crystals from Sri Lanka Mineralogical Record - Find Articles
It has a damaged region from which a small fragment was removed for optical, chemical, and X-ray study.
As these are the only euhedral crystals of sinhalite known to us, save the one from Burma, a description and comparison with the British Museum crystal seem appropriate.
The gemstones of Sri Lanka are found in ancient alluvial deposits eroded from Precambrian rocks of the Highland and Southwest groups.
findarticles.com /p/articles/mi_qa3672/is_199503/ai_n8727649   (873 words)

  
 Glossary carbonate sediment petrology
Euhedral refers to a single crystal or crystal fabric which shows well-defined typical crystallographic forms.
Stylolite a jagged, columnar surfaces in carbonate rocks which may be at any orientation relative to bedding; often associated with large amounts of insoluble material, and produced by solution and grain interpenetration.
Sucrose carbonate rocks that have appreciable intercrystal pore space and are composed dominantly of somewhat equant, uniformly sized, euhedral to subhedral crystals.
strata.geol.sc.edu /thinsections/Carbonate-glossary.html   (2104 words)

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