Nenadkevichite is a rare silicate mineral containing niobium)(Nb. It forms brown to yellow to rose colored orthorhombic dipyramidal crystals with a dull to earthy luster. It has a Mohs hardness of 2.86.
It was first reported in 1955 from a nepheline syenite pegmatite. In addition it has been reported from Mont Saint-Hilaire , Canada, Greenland ; and Zheltye Vody. It was named after Konstantin Avtonomovich Nenadkevich (1880–1963), Russian and geochemist.