Bismutotantalite

Bismutotantalite is a rare oxide mineral made up mainly of bismuth, tantalum, and oxygen. It is notable among oxide minerals for its very high density and refractive index. Its ideal chemical formula is BiTaO4, though the more general formula Bi(Ta,Nb)O4 reflects the fact that niobium can substitute for some of the tantalum in its structure. Bismutotantalite belongs to a small family of related minerals known as the stibiotantalite group, all of which share the general chemical pattern ABO4. Because chemically similar elements can swap places within this structure, bismutotantalite forms a solid solution series with bismutocolumbite (BiNbO4) as niobium substitutes for tantalum, and is related in the same way, through substitution of antimony (Sb) for bismuth, to stibiotantalite (SbTaO4).