Ferrocolumbite

Formula:  FeNb₂O₆

Origin of name:   From ferrous iron (Fe²⁺) and manganocolumbite

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:

Unit cell: 

Colour:  Black

Diaphaneity:

Luster:  Submetallic to weakly vitreous

Habit:  Crystals thin to thick tabular, short prismatic, equant or pyramidal; aggregates; massive, compact

Hardness:  6

Specific gravity:  4.63

Cleavage:  2; {010} distinct, {100} less distinct

Tenacity: 

Streak:  Black to brownish black

Synonyms/varieties:

Comments:  Series with ferrotantalite and with manganocolumbite