Columbite

Columbite, also called niobiteniobite tantalite and columbate [(Fe, Mn)Nb2O6], is a black mineral group that is an ore of niobium. It has a submetallic luster and a high density and is a niobate of iron and manganese.

This mineral group was first found in Haddam, Connecticut, in the United States. It forms a series with the tantalum-dominant analogue ferrotantalite and one with the manganese-dominant analogue manganocolumbite.

The iron-rich member of the columbite group is ferrocolumbite. Some tin and tungsten may be present in the mineral. Yttrocolumbite is the yttrium-rich columbite with the formula (Y,U,Fe)(Nb,Ta)O4. It is a radioactive mineral found in Mozambique.

It is the most widespread niobium mineral and makes for an important ore of the industrially useful metal. Niobium, Nb, is used in alloys for improved strength. It also has shown superconductive properties and is being studied with other metals for a possible breakthrough alloy in this new industrial field.

This alloy is a series within a series. The iron, manganese and magnesium amounts vary considerably without much effect on properties. However the end members are recognized as distinct minerals although collectors have found this to be rather cumbersome and generally prefer columbite to the non-unique names of ferrocolumbite, manganocolumbite and magnocolumbite.

As mineral specimens, columbite can be a nice addition to one’s collection. Good crystals are both complex and handsome. Although the color selection is usually limited too black to brown the luster is generally good.

These minerals are the most abundant and widespread of the naturally occurring niobates and tantalates and are important ores, their elements niobium and tantalum serving as constituents of corrosion-resistant metal alloys.

Columbite has the same composition and crystal symmetry (orthorhombic) as tantalite. In fact, the two are often grouped together as a semi-singular mineral series called columbite-tantalite or coltan in many mineral guides. However, tantalite has a much greater specific gravity than columbite, more than 8.0 compared to columbite’s 5.2.

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