Columbite

There are three columbites:
columbite-(Fe): Fe2+Nb2O6,
columbite-(Mg): MgNb2O6, and
columbite-(Mn): Mn2+Nb2O6
All of these are multiple oxides containing niobium, and members of the columbite group

Specific gravity: 5.3 - 8.1
Hardness: 6
Streak: Brown to black
Colour: Brownish black to black
Solubility: Insoluble in hydrochloric and nitric acid; slightly soluble in sulphuric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites

Columbite occurs in granitic rocks and pegmatites, associated with quartz, feldspars, mica, tourmaline, beryl, spodumene, cassiterite, hübnerite-ferberite, microlite and monazite.