Fergusonite is a mineral comprising a complex oxide of various rare earth elements. The chemical formula of fergusonite species is (Y,RE)NbO₄, where RE = rare-earth elements in solid solution with Y. Yttrium is usually dominant (the species fergusonite-(Y)), but sometimes Ce or Nd may predominate in molar proportion (species fergusonite-(Ce) and fergusonite-(Nd)). All the other rare earth elements are present in subordinate amount, and tantalum substitutes for some of the niobium. There are Fergusonite-beta-(Nd), Fergusonite-beta-(Y), Fergusonite-beta-(Ce) too, but they are classified as 04.DG.10 in the Nickel-Strunz system. The mineral has tetragonal crystal symmetry and the same structure as scheelite (calcium tungstate, CaWO₄), but can be metamict (amorphous) due to radiation damage from its small content of thorium. It is found as needle-like or prismatic crystals in pegmatite. It was named after British Politician and mineral collector Robert Ferguson of Raith (1767-1840).