Tantalite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Orthorhombic
    Chemistry : (Fe2+, Mn2+, Mg2+) (Ta, Nb)2O6
    Rarity : Uncommon


Tantalite forms a continuous series with columbite, hence the names columbo-tantalite or tantalo-columbite depending on the dominant element. It owes its name to the tantalum present as a major element in its chemical composition. These "minerals" have such varying chemical compositions that they have been promoted to groups and subdivided according to the dominant element into columbite-(Fe), columbite-(Mn) and colombite-(Mg) (columbite group), tantalite-(Fe) and tantalite-(Mn) (tantalite group). These minerals, difficult to distinguish from one another, are found especially in granitic pegmatites with rare elements, in particular sodium-lithium (sodolithic) and sodium-potassium (sodolithic potassium) pegmatites, where they are usually dark crystals of sometimes impressive size, weighing up to 15 kg. Heavy (density between 5.2 and 8 depending on the mineral), hard, and almost unalterable, these minerals are also very common in alluvium where their main operations are located. The minerals of the tantalite group are essential tantalum ores .

Tantalite from Kunar Province, Afghanistan

Tantalite from Kunar Province, Afghanistan

Tantalite from Kunar Province, Afghanistan

Twinned tantalite from Kunar Province, Afghanistan

Tantalite in the World

Tantalite-(Fe) : it occurs in short, often rectangular prismatic crystals ("matchbox" facies), also in large groups of subparallel crystals or in sheaves. From almost metallic to vitreous luster, tantalite-(Fe) is opaque, black in color. It provided large crystals in the American pegmatites of South Dakota (Upper Bear Gulch), and Austria (Spittal an der Drau).
 
Tantalite-(Mn) : it occurs in short prismatic crystals, often in rectangular prisms ("matchbox" facies), also in large groups of sub-parallel crystals or in sheaves. From an almost metallic luster to a very bright adamantine, tantalite-(Mn) is frequently translucent, brown to red for the strongly manganiferous terms, reddish black and opaque for the others. Superb twinned crystals, of a pronounced red and of decimetric size for a weight of several kilos, come from the pegmatites of Mozambique, in particular Muiâne. Very good samples also come from Tanco (Manitoba, Canada), Greenwood (Maine) and Richmond (Virginia).

Tantalite in France

Tantalite-(Fe) : in France the pegmatites of the Monts d'Ambazac in Haute-Vienne (Chanteloube, Chabannes, etc...) have yielded quite a number of crystals of modest size.
 
Tantalite-(Mn) : in France, manganotantalite has been described at the Beauvoir quarry (Echassières, Allier) as well as at Puy Bézin near Ussel (Corrèze).

Twinning

Tantalite twins commonly on {201} forming hearts and showing a delicate feather-like striation on {010}. This repeated twin can form pseudo-hexagonal trills. Twins on {203} are rarer and give similar heart shapes. Twinning on {501} and on {1 50 0} are very rare.

Fakes and scams

No scam known for this mineral.



Hardness : 6 to 6.5
Density : 6.65 to 7.95
Fracture : Irregular to sub-conchoidal
Trace : Black, yellow, red



TP : Translucent to opaque
RI : 2.140 to 2.430
Birefringence : 0.200
Optical character : Biaxial (+/-)
Pleochroism : Hard to observe
Fluorescence : None


Solubility : concentrated sulfuric acid
Magnetism : Paramagnetic
Radioactivity : None to low