columbite

(kə-lŭm'bīt')
n.
A black, red-brown, or colorless mineral, essentially (Fe, Mn)(Nb, Ta)₂O₆, the principal ore of niobium.

[COLUMB(IUM) + -ITE¹.]

A mineral with the composition (Fe,Mn)Nb₂O₆. Tantalum may substitute in all proportions for the niobium; and a complete series extends to the pure end-member tantalite [(Fe,Mn)Ta₂O₆], a relatively rare mineral. With a complete solid solution of iron and manganese, four end-member compositions are possible: FeNb₂O₆ (ferrocolumbite), MnNb₂O₆ (mangancolumbite), FeTa₂O₆ (ferrotantalite), and MnTa₂O₆ (mangantantalite).

Physical properties vary with composition. The specific gravity may range from 5.0 for MnNb₂O₆ to 5.4 for FeNb₂O₆; FeTa₂O₆ has a specific gravity of 7.9. The hardness of columbite on the Mohs scale is 6, while that of tantalite is 6.5. When the mineral is studied as a hand specimen, the color is black; however, the streak may be dark red to black. Manganoan varieties, end-member compositions rich in manganese, are often reddish brown. The luster is submetallic to weakly vitreous.

Columbite is a common accessory mineral in granitic pegmatites, and it may occur as a heavy mineral in placer deposits in streams. Minerals of the columbite-tantalite series are the most abundant and widespread of the natural columbates and tantalates, and columbite is the chief ore mineral of niobium. Niobium is used chiefly as an alloying element in the manufacture of specialty steels and alloys with nuclear and aerospace applications. See also Mineralogy; Niobium; Pegmatite.

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(Fe,Mn)(Nb,Ta)

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The noun has one meaning:

Meaning #1: a black mineral that is an ore of niobium and tantalum
  Synonym: niobite

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