Tantalite

a mineral of the group of multiple oxides; the extreme member of the isomorphic columbite-tantalite series. Its chemical composition is (Fe,Mn) (Ta,Nb)₂O₆. In tantalite, tantalum predominates over niobium in percent by weight. Varieties of tantalite are ferrotantalite, in which FeO: MnO > 3:1 and the FeO content reaches 14 percent, and manganotantalite, in which MnO:FeO > 3:1 and the MnO content reaches 14 percent. Ca, Mg, Sn, Ti, W, U, and Th are present as admixtures. Tantalite crystallizes in the orthorhombic system; it is of the columbite structural type. The crystals are tabular and acicular and the colors are black, grayish, brown, and red-brown. In the columbite-tantalite series, there is a regular change in physical properties with increasing Ta₂0₅ content; tantalite is harder (up to 6.5 on Mohs’ scale) and denser (7,000–8,200 kg/m³). Tantalite differs from columbite in its optical constants in the infrared region of the spectrum.

Tantalite is genetically associated with granites, rare-metal, muscovite, and quartz-feldspar pegmatites, carbonatites, and alkaline rocks. In pegmatites, tantalite crystallizes in a later stage than columbite, associating with albite, lepidolite, beryl, and other minerals. Tantalite is resistant to weathering and concentrates in placers, which are the main source for its extraction. It is used as an ore of tantalum.