Samarskite is a radioactive rare earth mineral series which includes samarskite-(Y) with formula: (YFe³⁺Fe²⁺U,Th,Ca)₂(Nb,Ta)₂O₈ and samarskite-(Yb) with formula (YbFe³⁺)₂(Nb,Ta)₂O₈ The formula for smarskite-(Y) is also given as: (Y,Fe³⁺,U)(Nb,Ta)O₄