Romer and Wright ( 1992) have shown that columbite-tantalite may accommodate considerable amounts of uranium (circa 500–1000 ppm) and exclude lead almost completely. The U-Pb systematics, however, are typically not straightforward; reverse discordance and excess scatter are very common (Romer and Smeds 1994, 1996, 1997 ).

 · columbite (niobite, tantalite) a mineral oxide (fe,mn) (ta,nb) 2 o 6; when ta > nb the mineral is called tantalite, but when ta < nb it is called columbite; sp. gr. 5.2–6.5, increasing with increasing ta content; hardness 6.0–6.5; orthorhombic; weakly magnetic; black or brownish-black; very dark red streak; sub-metallic lustre; crystals normally …

Formula: Mn2+Nb2O6 Colour: Black to brownish black, dark red-brown; reddish brown in transmitted light Lustre: Vitreous, Sub-Metallic Hardness: 6 Specific Gravity: 5.20 - 6.65 …

 · The generalized formula of columbite–tantalite of the deposit is (Mn 0.61 Fe 0.34) 0.95 (Nb 1.37 Ta 0.58 Ti 0.04 W 0.03 Sn 0.01) 2.03 O 6. Columbite–tantalite forms …

Due to their relatively high Hf contents (i.e., several hundreds to thousands of ppm), columbite-group minerals (CGMs) are suitable for Lu–Hf isotope analysis, which can provide new insights into the source of such minerals in combination with the U–Pb age of rare-metal deposits.However, few studies have reported Lu–Hf isotope data for CGMs. Tantalum is …

This unusually high dose was attributed to long-term annealing of α-recoil collision cascades back to the original structure. We have recently found zoned columbite–tantalite crystals …

Giles Columbite-Beryl Pegmatite, Spargoville, Coolgardie Shire, Western Australia, Australia Dimensions: 2.2 cm x 1.6 cm x 1.3 cm Largest Crystal Size: 1.9 cm Extra sharp black 1.9 cm tall terminated Columbite- (Fe) crystal on a small amount of matrix. Collected in 2002. Personal collection of Sharon Cisneros.

 · The dielectric properties of the columbite concentrate and its mixture 1:1 with sodium bicarbonate were characterized using the cavity perturbation method 22 from room temperature to 1000 °C with ...

 · The reaction-sintering process has proven to be a simple and effective method in preparing columbite NiNb 2 O 6 ceramics. A higher density could be obtained at lower sintering temperature by using NiO instead of 50%Ni (NO 3) 2 -50%NiO in the reaction with Nb 2 O 5. Download to read the full article text References

 · Columbite, also called niobite, niobite-tantalite and columbate, is a black mineral group that is an ore of niobium and tantalum. It has a submetallic luster and a high density and is a niobate of iron and manganese, containing tantalate of iron. Columbite and tantalite are collectively known as coltan in Africa.

 · The dielectric properties of the columbite concentrate and its mixture 1:1 with sodium bicarbonate were characterized using the cavity perturbation method 22 from room temperature to 1000 °C with...

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 · The columbite type LiNb 3 O 8 with micrometer sized crystallites shows initially 234 mA hg −1, however subsequent cycles cause rapid fading to 45 mA hg −1. In …

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 · Decentralized electrosynthesis of hydrogen peroxide (H 2 O 2) via oxygen reduction reaction (ORR) can enable applications in disinfection control, pulping and textile bleaching, wastewater treatment, and renewable energy storage. Transition metal oxides are usually not efficient catalysts because they are more selective to produce H 2 O.

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 · This paper reports experimental data on columbite solubility in model water-saturated Li- and F-rich silicic melts with different contents of alumina and alkalis. It was found that the columbite solubility is strongly affected by melt composition and is maximal in peralkaline melt. The maximum contents of Ta and Nb in subaluminous and …

Formula: Mn2+Nb2O6 Colour: Black to brownish black, dark red-brown; reddish brown in transmitted light Lustre: Vitreous, Sub-Metallic Hardness: 6 Specific Gravity: 5.20 - 6.65 Crystal System: Orthorhombic Member of: Columbite Group > Columbite Supergroup Name:

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 · It is most distinct in the subaluminous melts. The Nb/Ta ratio of melt usually decreases with decreasing temperature. The effect of pressure is relatively small. It was shown that columbite cannot crystallize on the liquidus of …

4.4 x 3.8 x 2.3 cm. A rare and very showy columbite-tantalite combination specimen from Pech. The lustrous, tabular, twinned, black columbite-tantalite crystals, 1.2 cm across, are very deftly framed within a cluster of pearlescent muscovite plates. Lustrous, snow-white cleavelandite blades below the columbites are a very nice accent. Ex. Herb ...

 · Moreover, among these eighteen Type 1 columbite spots, the 206 Pb/ 238 U ages of the rims of the individual columbite are similar to those of the core. For example, 241.0 Ma, 241.5 Ma, and 244.9 Ma ages of spots 1-1, 1-2, and 1-3, respectively, are similar within an individual columbite grain (no. 1), indicating that there is no age variation ...

 · The Brazilian Nuclear Agency (CNEN) rules all nuclear activity in Brazil as demanded by the Federal Constitution, articles 21, XXIII, and 177, V, and by the Federal Acts 4.118/62 and 10.308/2001.

Decentralized electrosynthesis of hydrogen peroxide (H 2 O 2) via oxygen reduction reaction (ORR) can enable applications in disinfection control, pulping and textile bleaching, wastewater treatment, and renewable energy storage.Transition metal oxides are usually not efficient catalysts because they are more selective to produce H 2 O. Here, it is shown …

 · columbite (niobite, tantalite) A mineral oxide (Fe,Mn) (Ta,Nb) 2 O 6; when Ta > Nb the mineral is called tantalite, but when Ta < Nb it is called columbite; sp. gr. 5.2–6.5, …