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COLUMBITE , a rare See also:mineral consisting of See also:iron niobate, FeNb206, in which the iron and niobium are replaced by varying amounts of See also:manganese and See also:tantalum respectively, the See also:general See also:formula being (Fe, Mn) (Nb, Ta)206. It was in this mineral that
See also:Charles Iatchett discovered, in 18or, the See also:element niobium, which he himself called See also:columbium after the See also:country (See also:Columbia or See also:America) whence came the specimen in the See also:British Museum collection which he examined. The See also:species . has also been called niobite. It crystallizes in the orthorhombic See also:system, and the See also:black, opaque crystals are often very
brilliant with a sub-metallic lustre. Twinned crystals are not uncommon, and there is a distinct cleavage parallel to the See also:face marked See also:bin the figure. Hardness 6; specific gravity 5.3. With increasing amount of tantalum the specific gravity increases up to 7.3, and members at this end of the See also:series are known as tantalite (FeTa2O6). Specimens in which the iron is largely replaced by manganese are known as manganocolumbite or manganotantalite, according as they contain more niobium or more tantalum. Columbite occurs as crystals and compact masses in See also:granite and See also:pegmatite at Rabenstein in See also:Lower See also:Bavaria,
the Ilmen Mountains in the Urals, Haddam in See also:Connecticut, and several other localities in the See also:United States; also in the See also:cryolite of See also:Greenland. Tantalite is from See also:Finland, and it has recently been found in some abundance in the deposits of cassiterite in the See also:tin-See also:- FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
- FIELD, CYRUS WEST (1819-1892)
- FIELD, DAVID DUDLEY (18o5-1894)
- FIELD, EUGENE (1850-1895)
- FIELD, FREDERICK (18o1—1885)
- FIELD, HENRY MARTYN (1822-1907)
- FIELD, JOHN (1782—1837)
- FIELD, MARSHALL (183 1906)
- FIELD, NATHAN (1587—1633)
- FIELD, STEPHEN JOHNSON (1816-1899)
- FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)
field of Greenbushes in the See also:Blackwood See also:district, Western See also:Australia.
Dimorphous with columbite and tantalite are the tetragonal minerals tapiolite (= skogbolite) and mossite, so that the four See also:form an isodimorphous See also:group with the general formula (Fe, Mn) (Nb, Ta)20s. Mossite is from a pegmatite vein near See also:Moss in See also:Norway, and tapiolite is from Finland. All these minerals contain tin in small amount. (L. J.
End of Article: COLUMBITE
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