A mineral of a black color, submetallic luster, and high specific specific gravity. It is a niobate (or columbate) of iron and manganese, containing tantalate of iron; -- first found in New England.

a black mineral that is an ore of niobium and tantalum

niobium bearing mineral (Fe,Mn)(Nb,Ta)2O6 containing 40-75% Nb2O5, 1-40% Ta2O5, 0.5-3% TiO2, 10-20% Fe