Cerium Ammonium Sulfate

“Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife.
It is the most common of the lanthanides, followed by neodymium, lanthanum, and praseodymium.
Today, cerium and its compounds have a variety of uses: for example, cerium(IV) oxide is used to polish glass and is an important part of catalytic converters. Cerium metal is used in ferrocerium lighters for its pyrophoric properties.”