Columbite is an ore of niobium, forming a series with tantalite, and forming in granitic pegmatites. The general formula for the chemical unit of columbite is (Fe,Mn)(Nb,Ta)2 O6. The crystal systems are orthorhombic and the colour is black/brown. Thet are rated 6 on the Mohs scale for hardness and have a specific gravity between 5.3 and 7.3. Niobium is also found in the ore pyrochlore. This ore forms again a series with a tantualum rich member – microlite. The general unit formula of pyrochlore is (Na,Ca)2 Nb2O6(OH,F). The crystal systems are isometric, with colour from brown through yellow/red-brown, orange and black. The hardness is 5-5.5 on the Mohs scale, and the specific gravity is 4.45 – 4.9.
The pricing of columbite is done on the basis of the combined amount of niobium contained, measured as diniobium pentoxide (Nb2O5) and the tantalum contained measured as ditantalum pentoxide (Ta2O5). The two pentoxides are summed to give the combined pentoxide (CPO) total, usually expressed as a percent by weight, but also readily converted to pounds of CPO. The internationally traded price is mainly quoted in US dollars per pound CPO. There is no exchange trading of niobium, and price is determined by negotiations between buyers and sellers.
Our traded columbite is physically processed to attain a CPO of > 50% typically. The average percentages by mass of niobium and tantalum pentoxide contained are 48.84% and 4.88% respectively.