A rare earth is an oxide of a rare earth element. Often rare earth elements themselves are loosely called "rare earths". Rare earth elements, or metals, are the lanthanides and actinides. They come from the f-block. They are: lanthanum, cerium, praseodymium, neodymium, ppromethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, lawrencium.