Generally, lanthanum, cerium, praseodymium, neodymium, promethium, samarium and europium are classified as light rare earth or Cerium ions rare earth; gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium are classified as heavy rare earth or Yttrium group rare earth.
Among the various rare varieties, the most valuable one is the 1930 Australian penny. This rare piece commands a high value and the ones in very good condition are in the range of two hundred thousand dollars. The
