which metal is the most expensive
Californium is a rare earth metal and does not occur naturally on the planet. It is a radioactive metallic chemical element with the symbol Cf and atomic number 98. Not only is a gram of Californium worth US$27 million, it is second only to antimatter when it comes to the most expensive materials in the world. The element was first made in the 1950s at the University of California Radiation Laboratory in Berkeley, hence the name Californium which it takes from its origins.