Results 161 to 170 of about 2,032 (202)
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Geochemical prospecting for beryl and columbite
Economic Geology, 1962Analyses of 39 muscovite samples from pegmatites in South Dakota, New Mexico, Colorado, and North Carolina, show a positive correlation between the presence of beryl and columbite-tantalite in the pegmatites, and concentrations of Be and Nb in the associated muscovite.
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Luminescence and energy transfer in the columbite structure
Materials Research Bulletin, 1985The luminescence properties of undoped and Eu/sup 3 +/- and Dy/sup 3 +/doped CdNb/sub 2/O/sub 6/ and CaNb/sub 2/O/sub 6/ are reported and discussed in connection with the luminescence of niobates and tungstates with wolframite and columbite structure. It is shown that these structures lead in principle to highly efficient luminescent materials. However,
G. Blasse, M.G.J. van Leur
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Compositional and structural systematics of the columbite group
American Mineralogist, 1995ABSTRACf The systematics of the columbite group have been studied to quantify variations in composition and structure. Multiple regression methods involving 89 heated samples and five synthetic equivalents of columbite-group minerals give equations that permit prediction of the effects of composition on unit-cell parameters for fully ordered samples ...
T. Scott Ercit +2 more
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Electrostatic energy of columbite/ixiolite
Nature, 1975A KNOWLEDGE of the crystal structure of an inorganic compound and the appropriate ionic charges is usually sufficient to allow the calculation of the electrostatic energy1–3. A more difficult situation is found in crystals where some or all of the cations are disordered so that on the average a particular cation site is occupied by two or more cations ...
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CATION ORDERING AND MICROSTRUCTURES IN COLUMBITE
2008The mechanism of the intracrystalline cation exchange reaction in a natural columbite sample from Kragero, with composition (Mn0.85Fe0.15)(Nb1.8Ta0.2)O6, has been characterised by means of TEM and HR synchrotron-radiation powder diffraction. In columbite, cations may occupy two different octahedral sites, with divalent cations preferring the A site and
Tarantino, SC +5 more
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Columbite from the Carrock Fell tungsten deposit
Mineralogical Magazine, 1981AbstractMinute crystals of columbite occur in tungstate ore in the quartz veins at Carrock Fell Mine. Accompanying wolframite crystals show pronounced niobium enrichment adjacent to growth faces. The columbite grains, however, occur as inclusions in minerals formed during metasomatic replacement of the wolframite.
B. Beddoe-Stephens, N. J. Fortey
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2001
The minerals of columbite-tantalite group have orthorhombic symmetry and general formula AB2O6, where A = Fe2+, Mn2+, Mg and B = Nb5+, Ta5+. Minor substitutions of Sn4+, Ti4+, Sc, W6+ and Fe3+ are also possible. A mineral sample from Tiltvika pegmatite, Nordland, Norway was investigated.
Tomašić, Nenad +2 more
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The minerals of columbite-tantalite group have orthorhombic symmetry and general formula AB2O6, where A = Fe2+, Mn2+, Mg and B = Nb5+, Ta5+. Minor substitutions of Sn4+, Ti4+, Sc, W6+ and Fe3+ are also possible. A mineral sample from Tiltvika pegmatite, Nordland, Norway was investigated.
Tomašić, Nenad +2 more
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Radioactive Columbite from Haddam, Conn.
Rocks & Minerals, 1953(1953). Radioactive Columbite from Haddam, Conn. Rocks & Minerals: Vol. 28, No. 3-4, pp. 156-156.
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A note on the occurrence of columbite in the Meldon aplite, Devonshire
Mineralogical Magazine and Journal of the Mineralogical Society, 1951During a departmental excursion to South Devon in April 1951, material was collected from the Meldon aplite quarry near Okehampton, to the north-west of the Dartmoor granite, which on examination has proved to contain the mineral columbite. The mineral is present only in very small amounts and as extremely minute crystals; nevertheless its presence is ...
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