Columbite
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Columbite, also called niobite, niobite-tantalite and columbate, with a general chemical formula of Nb₂O₆, is a black mineral group that is an ore of niobium. It has a submetallic luster, a high density, and is a niobate of iron and manganese. Wikipedia
Color: Black, brownish black
Cleavage: Distinct
Crystal class: Dipyramidal (mmm); H-M symbol: (2/m 2/m 2/m)
Crystal system: Orthorhombic
Fracture: Sub Conchoidal: Fractures developed in brittle materials characterized by semi-curving surfaces
IMA symbol: Clb
Luster: Sub-metallic