tantalite

n.
A black to red-brown mineral, (Fe,Mn)(Ta,Nb)₂O₆, distinguished from columbite by the predominance of tantalum over niobium and used as an ore of both elements.

[TANTAL(UM) + -ITE¹.]

A mineral with compositon (Fe,Mn)Ta₂O₆, an oxide of iron, manganese, and tantalum. Niobium substitutes for tantalum in all proportions; a complete series extends to columbite (Fe,Mn)Nb₂O₆. Pure tantalite is rare. Iron and manganese vary considerably in their relative proportions. Tantalite crystallizes in the orthorhombic system and is common in short prismatic crystals. The hardness is 6 on Mohs scale, and the specific gravity 7.95 (pure tantalite). The luster is submetallic and the color iron black. Tantalite is the principal ore of tantalum. It is found chiefly in granite pegmatites and as a detrital mineral, in some places in important amounts, having weathered from such rocks. The chief producing areas are the Congo and Nigeria. See also Columbite; Hardness scales; Niobium; Tantalum.

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(Fe,Mn)(Ta,Nb)
Orthorhombic -- Rhombic bipyramidal

Environment

Pegmatite dikes.

Crystal description

Always in crystals or crystal aggregates. Sometimes in well-formed rectangular crystals ranging from very thin to almost equidimensional. Parallel (graphic) growths in quartz or feldspar have been noted.

Physical properties

Black to red-brown and colorless. Luster submetallic to resinous; hardness 6; specific gravity 5.2-8.0; streak black to brown to white; fracture uneven; cleavage front and side pinacoid. Brittle; opaque to translucent or transparent.

Composition

The two names are applied to the end-members of a continuous mineral series ranging from an almost pure niobate of iron and manganese to an almost pure tantalate of iron and manganese. The niobium or tantalum oxide will range from 78% to 86%.

Tests

Infusible and insoluble. Some iron-rich varieties weakly magnetic.

Distinguishing characteristics

These minerals are best recognized by the high gravity of the tantalum-rich varieties. The fracture faces are commonly iridescent, bluish. In their occurrence they can be confused with magnetite (but are less magnetic), with uraninite (but are not radioactive), with black tourmaline or cassiterite (but are higher in gravity), and wolframite (which has a more perfect cleavage). Columbite and tantalite are separated on the basis of density; tantalite begins to prevail at about a 6.6 specific gravity.

Occurrence

This pair is found only in pegmatites or in gravels derived from pegmatites. They are the chief ores of niobium and tantalum. The representative in some pegmatites will be high in niobium and in others it will be richer in tantalum. With regional variation, both minerals may even be present in a single pegmatite when there is a long series of stages of rare mineral deposition. In Brazil, however, tantalite is more abundant in Ceará and the north, columbite in Minas Gerais. These are common and widespread minerals, found in commercial quantities in Mozambique, Western Australia, and Brazil. In all of these localities they are also recovered from alluvial deposits, where they have been washed out of decomposing pegmatites. They are commonly associated with cassiterite and with rare-earth minerals.

Fine crystals, up to several inches in length, have been found in the New England pegmatites. Small manganotantalites or manganocolumbites are often associated with the secondary albite feldspar cleavelandite at such pegmatites as Newry, Maine, and Amelia, Virginia. This type is brown and translucent. A white bismuth and antimony-bearing (bismuto/stibio-) tantalite variety, in fragments resembling cerussite in appearance, has been found in Brazil and Mozambique.

Fine columbite crystals have been found in North Carolina around Spruce Pine; New Mexico; the Black Hills, in heavy masses; and the Pikes Peak district of Colorado.

Remarks

Columbite got its name from columbium, the former American name for the element now known universally as niobium. Columbite often forms in parallel crystal growths with a related mineral, samarskite (next). Greater resistance of columbite to alteration makes the columbite areas of these combinations look blacker and fresher than the brown weathered samarskite. Particularly good examples of this association have come from the Divino de Ubá pegmatite in Minas Gerais, Brazil.

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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: a mineral consisting of tantalum oxide of iron and manganese that occurs with niobite or in coarse granite; an ore of tantalum

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