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Topic: Rhombohedral

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	Earth Science World Image Bank
		Borates; Calcite; Calcium Carbonate; Carbonates; Galena; Hexagonal; Mineralogy; Nitrates; Rhombohedral Cleavage; Sedimentary Mineral
		Cyclosilicates; Hexagonal; Hydrous Copper Silicate; Mineralogy; Prismatic; Rhombohedral; Silicates
		Borates; Calcite; Calcium Carbonate; Carbonates; Cleavage; Crystals; Hexagonal; Mineralogy; Nitrates; Rhombohedral; Sedimentary Mineral
	www.earthscienceworld.org /imagebank/search/results.html?Keyword=Rhombohedral (68 words)

	Process for producing rhombohedral system boron nitride - Patent 4419335
		Rhombohedral system boron nitride is produced by heating a boron material selected from the group consisting of boron oxide, boric acid and an oxygen-containing boron compound capable of forming boron oxide when heated, at a temperature of from 1200.degree.
		This rhombohedral system boron nitride was observed by an electron microscope, and it was found to be a coalescence of beard-like crystals elongated in the direction of the c-axis with hexagonal system notation and having good crystallinity and a diameter of about one micron.
		Each rhombohedral system boron nitride obtained in each Example was mixed with copper powder, and exposed to a pressure region for the formation of cubic system boron nitride by a impact-pressure method.
	www.freepatentsonline.com /4419335.html (1937 words)

	ASYMMETRIC - Online Information article about ASYMMETRIC
		common use; rhonlbohedral axes being usually used for crystals of the rhombohedral division, and hexagonal axes for those of the hexagonal division; though sometimes either one or the other set is employed in both divisions.
		Rhombohedral axes are taken parallel to the three sets of edges of a rhombohedron (fig.
		In the rhombohedral or trigonal division of the hexagonal system there are seven symmetry-classes, all of which possess a single triad axis of symmetry.
	encyclopedia.jrank.org /ARN_AUD/ASYMMETRIC.html (705 words)

	NationMaster - Encyclopedia: Rhombohedral (Site not responding. Last check: )
		In crystallography, the rhombohedral (or trigonal) crystal system is one of the 7 lattice point groups.
		In the rhombohedral system, the crystal is described by vectors of equal length, all three of which are not mutually orthogonal.
		However, in the case of the HCP lattice a rectangular boundary box was used, and a rhombohedral boundary box was used in the case of the RH lattice.
	www.nationmaster.com /encyclopedia/Rhombohedral (344 words)

	rhombohedral - OneLook Dictionary Search
		We found 13 dictionaries with English definitions that include the word rhombohedral:
		Tip: Click on the first link on a line below to go directly to a page where "rhombohedral" is defined.
		Phrases that include rhombohedral: rhombohedral iron ore, rhombohedral system, octahedral dodecahedral or rhombohedral, rhombohedral cleavage, rhombohedral division
	www.onelook.com /?w=rhombohedral&ls=a (139 words)

	Procedure
		The Cartesian coordinates of each atom in a lattice were determined by the chosen size of the cell length, the lattice type, and the number of atoms, with the RH lattice requiring the specification of a single rhombohedral angle as well.
		Illustrations of lattice expansions, as well as of the variation of the rhombohedral angle at a fixed cell parameter, may be viewed by consulting the Supplementary Materials section.
		However, in the case of the HCP lattice a rectangular boundary box was used, and a rhombohedral boundary box was used in the case of the RH lattice.
	www.cooper.edu /engineering/chemechem/ijc/procedure.htm (1036 words)

	A rhombohedral phase of lipid containing a membrane fusion intermediate structure Biophysical Journal - Find Articles
		Diphytanoyl (3,7,11,15-tetramethylhexadecanoic) phosphatidylcholine (DPhPC) was found to exhibit a structure of rhombohedral symmetry between a lamellar phase and an inverted hexagonal phase as a function of hydration.
		In this paper we report the x-ray experiment that recorded the diffraction patterns of rhombohedral symmetry and the subsequent reconstruction of the electron density distribution from the data.
		We made use of a small range of hydration in which the rhombohedral structure existed, and applied a swelling method to help determine the relative phases of the diffraction peaks along the crystal axis perpendicular to the hexagonal base.
	www.findarticles.com /p/articles/mi_qa3938/is_200303/ai_n9193762 (836 words)

	materials science 01
		is found to exhibit extremely unusual features which include pressure independence of the Curie temperature in the orthorhombic phase, a re-entrance of the rhombohedral phase at low temperatures, and a change of the type of the magnetic phase transition from second to first-order at the intersection of the structural and magnetic phase boundaries.
		One of the key features of the phase diagram is that, due to the peculiar "Z"-shape of the structural phase-boundaries near the intersection, some of the lines of the phase-transitions cannot be seen by pure temperature variations.
		In the rhombohedral phase the "easy" direction of compression is the three-fold axis, which is at an angle to the Mn-O-Mn bonds, so that the Mn-O-Mn bond angle is more easily affected by applied pressure.
	www.ill.fr /AR-97/page/20magnet.htm (1066 words)

	Frequency of Quartz Twins
		Typical etch-figure patterns on the rhombohedral faces of Dauphiné twinned crystals are shown in Fig 2.
		All observations were confined to the rhombohedral faces of crystals except in the case of those from Herkimer County, N. This was necessary in most cases because of the lack of development of prism faces or because the prism faces were too striated or otherwise roughened for etching.
		Typical twin boundaries on the rhombohedral faces of the Arkansas crystals are shown in Fig.
	www.minsocam.org /MSA/collectors_corner/arc/qtztwin.htm (6204 words)

	Intro to Minerals: Crystal Class and System
		The rhombohedral crystal form is produced only by members of the trigonal and rhombohedral divisions of the hexagonal crystal system.
		The rhombic pyramidal crystal class is thus a member of the orthorhombic crystal system, the tetragonal pyramidal class is a member of the tetragonal crystal system, and the trigonal and hexagonal pyramidal classes are members of the rhombohedral (trigonal) and hexagonal divisions of the hexagonal crystal system respectively.
		It is thus apparent that the characteristic symmetry element of the isometric crystal system is the possession of four 3-fold axes of rotational symmetry, while the characteristic symmetry element of the rhombohedral division of the hexagonal crystal system is the possession of a single 3-fold axis of rotational symmetry.
	dave.ucsc.edu /myrtreia/crystal.html (4278 words)

	The Rhombohedral Unit Cell (Site not responding. Last check: )
		The Rhombohedral unit cell is a special case of a hexagonal cell
		To calculate the rhombohedral cell parameters and indexing:
		NB In most cases in the literature you will find rhombohedral cells described using the hexagonal parameters, because it is much easier to visualize and to index that way.
	imr.chem.binghamton.edu /444/part_I/sld047.htm (84 words)

	Calcite and Dolomite
		The best way to tell one from the other is the acid test: a drop of 1 M HCl on calcite produces an instant, obvious fizz; a drop on dolomite produces slow or no obvious bubbling.
		It is an excellent example of the rhombohedral cleavage of calcite (three cleavage planes, none at right angles).
		The calcite is readily identified by its rhombohedral cleavages displayed near the bottom of this photograph.
	www.pitt.edu /~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Calcite_Dolomite.html (231 words)

	calcite.html
		PEPIN COUNTY: Small clear rhombohedral crystals of calcite occur in vugs in dolostone with drusy dolomite and goethite pseudomorphs after both pyrite and marcasite in a quarry north of Stockholm, NW 1/4 NW 1/4 sec.
		- Travertine and small clusters of steep rhombohedral calcite crystals of white to pale yellow color occur in the Prairie du Chien group dolostones exposed in a quarry on Cady Creek, SE of Spring Valley in the SE 1/4 SW 1/4 SE 1/4 sec.
		- Calcite occurs as travertine and rhombohedral crystals in a quarry south of Elmwood on County P in SE 1/4 SE 1/4 sec.
	www.uwrf.edu /~wc01/calcite.htm (2980 words)

	A Rhombohedral Phase of Lipid Containing a Membrane Fusion Intermediate Structure -- Yang and Huang 84 (3): 1808 -- ...
		FIGURE 2 A complete diffraction pattern for the rhombohedral phase was obtained by a combination of three CCD recordings.
		The reciprocal lattice of rhombohedral symmetry is composed of a stack of hexagonal layers stacked up in the ABCABC...
		(rhombohedral) phase was not observed in previous studies of
	www.biophysj.org /cgi/content/full/84/3/1808 (4462 words)

	Results and Discussion
		Also, rhombohedral angles of 55 and 65 degrees are plotted here because an accurate minimum angle could not be obtained from such rough data.
		This would not be true for a rhombohedral lattice in general, but a rhombohedral lattice with an angle of approximately 60 degrees possesses a great amount of symmetry (a rhombus with a sixty-degree angle is equivalent to two equilateral triangles).
		At lower temperatures and pressures, the rhombohedral lattice is favored.
	www.cooper.edu /engineering/chemechem/ijc/resdis.htm (1842 words)

	Calcite (Site not responding. Last check: )
		A cleavage fragment of calcite showing its typical rhombohedral cleavage.
		A complex growth of rhombohedral calcite from Mount Vernon, Indiana.
		Rhombohedral pinkish crystals of Calcite with minor amounts of Quartz from Peru.
	www.gc.maricopa.edu /earthsci/imagearchive/calcite.htm (268 words)

	Crystallographic Topology - Cubic Groups
		The seven rhombohedral trigonal subgroups of the cubic groups are shown in the bottom row of the figure with their space group symbols and simplest lattice complex in the top row of each box.
		The index-3 subgroups (monoclinic/triclinic) of the rhombohedral groups are indicated on the middle line and the respective ITCr numbers on the bottom line of each box.
		The divider strip between the cubic and rhombohedral groups gives the point groups for all the groups involved in each column, with the cubic/orthorhombic (or tetragonal) to the left and the rhombohedral/monoclinic (or triclinic) to the right.
	www.ornl.gov /sci/ortep/topology/cubicgsg.html (1827 words)

	Friedelite, Schalerite, and Related Minerals
		The members of the group are rhombohedral hemimorphic, as determined by crystallographic and X-ray
		In column 4 the friedelite analysis carries a small amount by arsenic trioxide indicating that it is probably a "connecting link" with the related arsenic-bearing schallerite.
		Friedelite is rhombohedral hemimorphic, with a perfect basal cleavage showing a pearly luster on the cleavage plane.
	www.minsocam.org /msa/collectors_corner/arc/frankliniv.htm (1458 words)

	Colorado Gem and Mineral Company
		Quartz crystals at the Four Peaks Arizona mine are found in a breccia zone and many unique habits of quartz are found only at this locale.
		Some have overgrowths of clear quartz over amethyst, others include amethyst crystals with "C-faces", a flat pinacoid where a pointed junction of rhombohedral faces should appear.
		Copyright © 1999 - 2000 Colorado Gem and Mineral Co.
	www.coloradogem.com (605 words)

	The Rhombohedral Lattice (Site not responding. Last check: )
		The rhombohedral (R) cell presents special problems in visualization.
		To bring out the hexagonal nature of its lattice, and the relationship between rhombohedral crystals and ordinary trigonal or hexagonal crystals, the R cell is often represented as at right, with two interior points equally spaced along a diagonal.
		It is the only Bravais lattice cell with more than one interior point.
	www.uwgb.edu /dutchs/symmetry/rhombo-lattice.htm (285 words)

	Mineral Specimens / South America - Fabre Minerals (Site not responding. Last check: )
		Rhodochrosite forms rhombohedral crystals that have zonal changes of color and are scattered over a matrix of Pyrite, Sphalerite and Quartz crystals.
		TH13I0: Group of rhombohedral crystals with zoned changes of color, more intense at the center of the crystal and clearer near the edges.
		Notice the zonation of the color corresponding to different phases of growth, darker at the center of the crystal with alternating zones of different shades of pink nearer the edges.
	www.fabreminerals.com /specimens/SAM-south-america-mineral-specimens.php (3320 words)

	Stability of magnesiowustite in Earth's lower mantle -- Lin et al. 100 (8): 4405 -- Proceedings of the National Academy ...
		(101), (104), and (110) peaks of the rhombohedral phase (Fig.
		FeO transforms to a rhombohedral structure at pressures above 18 GPa at 300 K (5) and then to the NiAs or anti-NiAs structure (6-8).
		Because the rhombohedral phase of wüstite is stable
	www.pnas.org /cgi/content/full/100/8/4405 (2371 words)

	Magnesite (Site not responding. Last check: )
		Rhombohedral crystal of Magnesite measuring about 2" from left to right.
		CRYSTAL GROWTH AND HABITS Individual crystals are rare for magnesite but when they form they are rhombohedral or scalenohedral.
		BREAKABILITY Crystals have rhombohedral cleavage otherwise the massive varieties have an uneven fracture.
	www.gc.maricopa.edu /earthsci/imagearchive/magnesite.htm (82 words)

	Dolomite
		The sample has excellent rhombohedral form with dull pearly luster.
		Calcite and Dolomite are rhombohedral carbonates but dolomite is denser and has a higher refractive index.
		Magnesite is another carbonate mineral with rhombohedral cleavage.
	www.und.edu /instruct/mineral/geol318/webpage/raths (1061 words)

	Calcite (Rhombohedral Cleavage Pieces) - Bag of 10 (3 cm x 4 cm Specimens) ~ Minerals ~ Rock & Mineral Specimens ~ Nasco
		NASCO packages its bulk Rock and Mineral Specimens in both 1-kg packages and packages of ten 3 cm x 4 cm specimens.
		The picture represents one sample from both the large 1-kg package and the small Bag of 10 (3 cm x 4 cm specimens).
		Orders from outside the United States may be charged additional distributor, customs, and shipping charges.
	www.enasco.com /ProductDetail.do?sku=SB10587M (201 words)

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