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THE MINERAL TANTALITE

  • Chemical Formula: (Fe, Mn)(Ta, Nb)2O6, Iron Manganese Tantalum Niobium Oxide.
  • Class: Oxides and Hydroxides
  • Uses: An ore of tantalum and niobium and as mineral specimens.
  • Specimens


Tantalite is the most widespread tantalum mineral and makes for an important ore of the industrially useful metal. Tantalum is used in alloys for strength and higher melting points, in glass to increase the index of refraction, and in surgical steel, as it is non-reactive and non-irritating to body tissues.

Tantalite forms a series with the mineral columbite. In fact the two are often grouped together as a semi-singular mineral called columbite-tantalite in many mineral guides. A series is where two or more elements can occupy the same places within a crystal structure and their respective percentages can then vary. The two minerals of this series have similar properties since they have the same structure and similar chemistries (tantalum and niobium are very similar elements). Tantalite is the more tantalum rich end member and columbite is the more niobium rich end member. Niobium had been called columbium hence the name columbite.

Tantalite's greatest difference from columbite is its much greater specific gravity, 8.0+ compared to columbite's 5.2. Other properties that vary slightly are color, transparency and streak. Both minerals can be found more or less together in granitic pegmatites rich in lithium and phosphorus minerals with columbite concentrated at the edges of the pegmatite and tantalite enriched in the core.

Tantalite has a series of its own. The iron and manganese amounts vary considerably without much effect on properties. However the two end members are recognized as distinct minerals although collectors have found this to be rather cumbersome and generally prefer tantalite to the non-unique names of ferrotantalite and manganotantalite.

Tantalite has a dimorphic relationship to another mineral called tapiolite. A dimorph is a mineral that has the same chemistry but a different structure. Tapiolite has a tetragonal structure as opposed to the orthorhombic structure of tantalite although it has exactly the same chemistry, (Fe, Mn)(Ta, Nb)2O6.

As mineral specimens, tantalite 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. Manganese rich tantalites can be brown and translucent.

PHYSICAL CHARACTERISTICS:

  • Color is dark black, iron-black to dark brown or even reddish brown.
  • Luster is submetallic to almost resinous.
  • Transparency: Crystals are nearly opaque being transparent in thin splinters.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include stubby prismatic crystals with complexly faceted or rounded terminations. Also very flat tabular crystals sometimes aggregated together in parallel or nearly parallel groups. Can also be granular and massive.
  • Cleavage is good in one direction.
  • Fracture is subconchoidal.
  • Hardness is 6 - 6.5
  • Specific Gravity is approximately 8.0+ when pure (very heavy for non-metallic minerals).
  • Streak is brownish-red to black.
  • Other Characteristics: Some specimens may show a bluish iridescent tarnish and demonstrate weak magnetism.
  • Associated Minerals include albite, spodumene, cassiterite, microcline, lepidolite, apatite, beryl, microlite, tourmalines and amblygonite.
  • Notable Occurrences include Newry, Maine; San Diego Co., California; Colorado and Amelia, Virginia, USA; Renfrow County, Ontario, Canada; Madagascar; Sweden; Norway and Finland.
  • Best Field Indicators are crystal habit, streak, associations and specific gravity.

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