Manganotantalite

Manganotantalite is a mineral with very high density so even small gems are relatively heavy. It also has high dispersion and makes for a beautiful gem when properly cut although gems are usually just translucent. Gems are very rare and difficult to cut because of the cleavage.

The main sources of gemmy to semi-gemmy crystals are Konar Province, Afghanistan; Alto do Giz pegmatite, Rio Grande do Norte, Northeast Region, Brazil; Murrua, Alto Ligonha District, Zambezia Province, Mozambique; and Mbarara District, Uganda.

Crystallography: Orthorhombic – Dipyramidal
Crystal Habit: Crystals short prismatic or equant, also tabular; in groups of parallel or subparallel crystals; massive (by analogy to Ferrocolumbite).
Twinning: On [021] and [023], may produce pseudohexagonal trillings

 

Cleavage: [100] Distinct, [010] less Distinct
Fracture: Sub-Conchoidal to Irregular/Uneven
Tenacity: Brittle
Hardness (Mohs): 6.0
Density: 6.65 – 8.00 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive

 

Color: Pink to nearly Colorless, Redish Brown to Black
Transparency: Opaque to Translucent
Luster: Vitreous, Sub-Metallic
Refractive Index: 2.14 – 2.34  Biaxial ( + )
Birefringence: 0.080 – 0.200
Dispersion: Strong; r < v
Pleochroism: Strong; X = red, Y = red brown, Z = orange