Gadolinite is a mineral of a nearly black color and vitreous luster, and consisting principally of the silicates of cerium, lanthanum, neodymium, yttrium, beryllium, and iron with formula: (Ce,La,Nd,Y)₂FeBe₂Si₂O₁₀. Called gadolinite-(Ce) or gadolinite-(Y) depending on the prominence of the variable element composition.