cerium

on earth cerium is almost as abundant as copper (29) and is quite inexpensive especially in the form of cerium oxide widely used as an abrasive powder for polishing glass . cerium metal  is pyrophoric  witch
meaning that it can catch fire when scratch,file or grind it. in practice that dose not mean the hole lump caches fire but rather that the shavings burn as formed making the material very sparky . not surprisingly this makes cerium useful in liter flints where is highly pyrophoric nature is moderated by alloying it with iron (26).
 large lumps of undiluted mischmetal  lanthanum-cerium mixtures described under lanthanum (57) are used in movie special effects to create  large sparks.cerium has a atomic number of 58 atomic mass of 140 and atomic symbol of ce.