Bismutotantalite Value, Price, and Jewelry Information


Bismutotantalite - Madagascar
“Bismutotantalite,” Madagascar, 0.5 cts. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Extremely rare as a cut gem, even in very complete collections. Manu of the minerals in the tantalite group have been faceted; bismutotantalite is perhaps the rarest of them all. The color is attractive, but low hardness and good cleavage make use in jewelry unadvisable.

Bismutotantalite Value

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Bismutotantalite Information

DataValue
NameBismutotantalite
Crystallography Orthorhombic. Crystals sometimes large; massive; stream pebbles.
Colors Light brown to black
Luster Adamantine to submetallic
Fracture Subconchoidal. Brittle.
Hardness 5
Specific Gravity 8.84 (Brazil)
Birefringence 0.040
Cleavage Perfect 1 direction.
Dispersion No data
Stone SizesCut gems always small, less than 5 carats
Luminescence None
Spectral Not diagnostic.
Formula (Bi, Sb) (Ta, Nb)O4
Pleochroism No data

STREAKYellow-brown to black

OPTICS: α= 2.388; β = 2.403; γ = 2.428

Biaxial (+), 2V = 80°

OCCURRENCE: Pegmatites.

Gamba Hill, Uganda; Acari, Brazil.

COMMENTS: Extremely rare as a cut gem, even in very complete collections. Manu of the minerals in the tantalite group have been faceted; bismutotantalite is perhaps the rarest of them all. The color is attractive, but low hardness and good cleavage make use in jewelry unadvisable.

NAME: On account of the composition.