This rare metal occurs in small proportions in a few uncommon minerals, notably in gadolinite, which contains about 8 1/3 per cent. of the oxide, and in cerite (less than 4 per cent.) It is extremely difficult to isolate it from the other rare metals with which it is associated. Marignac prepared it in the metallic state by heating the chloride with potassium, obtaining it in the form of a powder or very small globules; while Hillebrand and Norton procure it in larger quantities by electrolysing the. fused chloride. It most resembles lanthanum, but has a darker colour its sp. gr. is 6.544. On exposure to the air, it tarnishes yellow, and filings of it burn with great brilliancy when held in a flame.