Gadolinite is a mineral of a nearly black color and vitreous luster. consists 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 (namely, Y if it has more yttrium, and Ce if it has more cerium).
Gadolinite is fairly rare, but it forms attractive crystals that some collectors desire. Its hardness is between 6.5 and 7, and its specific gravity is between 4.0 and 4.7. It fractures in a conchoidal pattern. The mineral's streak is grayish-green. It is also Pyrognomic, which means that it becomes incandescent at a relatively low temperature