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.
TANTALITE specimens:
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TANTALITE specimen tnt-1
$ 900.00
Dims: 3.6" x 2.0" x 1.6" (9.1 x 5.1 x 4.1 cm)
Wt: 3.59 oz. (101.9
Cruzeiro Mine, Minas Gerais, Brazil
A single Tantalite crystal is nestled in a matrix made up of intergrown clusters of crystalline lepidolite. It has dimensions of 1.0 x 0.6 x 0.4" (2.5 x 1.5 x 1.0 cm), and is in excellent condition, showing almost no damage. Though somewhat disjointed due to its intergrowth with the lepidolite, the crystal's form is nonetheless excellent, with well-defined edges and clean, though often striated faces that show a submetallic luster. One can easily see that it is double-terminated. It is opaque and has a black color, but shows colorful iridescence at certain angles. Adjacent to the Tantalite is a prismatic elbaite crystal, whose form is also somewhat disjointed. It shows considerable damage in the form of breakage planes; one of these
no photo
tnt-1 ($900.00)
Cruzeiro Mine, Minas Gerais, Brazil
TANTALITE specimen tnt-2
$ 36.00
Dims: 1.3" x 0.8" x 0.8" (3.3 x 2.0 x 2.0 cm)
Wt: 16.2 g
Quixaba Mine, Frei Martinho, Paraiba, Brazil
At least 2 Tantalite crystals are partially embedded in the quartz matrix of this specimen. They are of the manganese-rich variety of Tantalite that is known simply as Manganotantalite. Only one of these crystals appears to be complete; it is not fully exposed, and what is visible has dimensions of 0.3 x 0.2 x 0.1" (8 x 5 x 3 mm). It shows reasonably good orthorhombic prismatic form, and has a deep red coloration with a hint of brown and a bright, pearly luster. Besides the quartz, there is a small amount of muscovite at the crystal's base.
no photo
tnt-2 ($ 36.00)
Quixaba Mine, Frei Martinho, Paraiba, Brazil
TANTALITE specimen tnt-3
$ 48.00
Dims: 1.5" x 0.8" x 0.5" (3.8 x 2.0 x 1.3 cm)
Wt: 14.9 g
Quixaba Mine, Frei Martinho, Paraiba, Brazil
This small thumbnail specimen consists of at least 4 Manganotantalite crystals that are embedded in a pegmatite base. These crystals are in moderately good condition, as the largest one is obviously damaged and missing part of its termination. This largest crystal has visible dimensions of 0.8 x 0.3 x 0.1" (2.0 x 0.8 x 0.3 cm), and like the others, shows a warped but definite orthorhombic prismatic form and a pearly luster. It has a brownish-red coloration and would likely be transparent if it was not so intensely internally-fractured; it is translucent at the least, though. Some of the crystals seem to show good form, but are almost completely covered by the base rock, which protected them. As the base rock does not react to concentrated HCl, I am rather certain that it consists almost entirely of a feldspar.
no photo
tnt-3 ($ 48.00)
Quixaba Mine, Frei Martinho, Paraiba, Brazil
TANTALITE specimen tnt-4
$ 48.00
Dims: 1.3" x 1.3" x 1.0" (3.3 x 3.3 x 2.5 cm)
Wt: 1.13 oz. (32.1 g)
Quixaba Mine, Frei Martinho, Paraiba, Brazil
This small specimen consists of an incomplete Manganotantalite crystal that is partly embedded in a massive quartz matrix. The "crystal" has dimensions of 0.5 x 0.4 x 0.2" (1.3 x 1.0 x 0.5 cm) and is broken on 2 ends; however, one of these ends is partly embedded in the host rock, so maybe some of its termination has been left intact. The Manganotantalite has a deep red-black coloration with a hint of brown and a bright, adamantine luster that shows some almost metallic highlights. It appears to be essentially opaque. There is also some pale green muscovite present on the specimen that has a few odd tendencies to it; it appears to have filled random hollows in the host rock, and apart from its flaky, micaceous consistency, shows no actual crystalline form!
no photo
tnt-4 ($ 48.00)
Quixaba Mine, Frei Martinho, Paraiba, Brazil
TANTALITE specimen tnt-6
$ 85.00
Dims: 2.6 x 1.8 x 1.0" (6.6 x 4.7 x 2.5 cm)
Wt: 3.5 oz. (99 g)
Mount Kharitha, Kala Darrah Pech, Kunar Province, Pakistan
A single partial Tantalite crystal is partly embedded in the pegmatite host of this hand specimen. It has visible dimensions of 1.3 x 1.1 x 0.6" (3.2 x 2.9 x 1.5 cm) and is in merely fair condition, as it shows a large amount of relatively fresh damage. However, some slight healing may have occurred prior to mining, as I keep seeing what appear to be crystalline striations on some of the broken faces. Where intact, it shows good orthorhombic prismatic form, though old, healed-over damage has warped its form a bit. It has a brown-black color and a bright, vitreous luster, but where it has been weathered, the color is a paler, dark brown and the luster is dull. The pegmatite base also contains a few veins of pale smoky quartz.
no photo
tnt-6 ($ 85.00)
Mount Kharitha, Kala Darrah Pech, Kunar Province, Pakistan
TANTALITE specimen tnt-5
$ 282.00
Dims: 2.4 x 1.6 x 1.4" (6.1 x 4.1 x 3.5 cm)
Wt: 4.6 oz. (129 g)
Mount Kharitha, Kala Darrah Pech, Kunar Province, Afghanistan
A cluster of heavily-intergrown Tantalite prisms is partly embedded in the pegmatite base of this hand specimen. The crystals are in fair condition, as the largest ones are heavily cleaved and incomplete. These large crystals tend to measure about 0.5" (1.3 cm) in diameter- the rest are considerably smaller and are quite intergrown with the two aforementioned crystals. All show excellent orthorhombic form, a brown-black color and a dull, almost submetallic luster where intact. Where they are damaged, they show a very pronounced and deep red-brown coloration and a pearly luster.
no photo
tnt-5 ($282.00)
Mount Kharitha, Kala Darrah Pech, Kunar Province, Afghanistan
 

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