Wiktionary
nenadkevichite
n. (context mineralogy English) A rare silicate mineral containing niobium.
Wikipedia
Nenadkevichite
Nenadkevichite is a rare silicate mineral containing niobium with formula: ( Na, Ca)( Nb, Ti) Si O·2 HO. It forms brown to yellow to rose colored orthorhombic dipyramidal crystals with a dull to earthy luster. It has a Mohs hardness of 5 and a specific gravity of 2.86.
It was first reported in 1955 from a nepheline syenite pegmatite in the Kola Peninsula. In addition it has been reported from Mont Saint-Hilaire, Canada; the Ilimaussaq complex, Greenland; Windhoek District, Namibia; and Zheltye Vody, Ukraine. It was named after Konstantin Avtonomovich Nenadkevich (1880–1963), Russian mineralogist and geochemist.