Two Elements

RUBIDIUM
The symbol is Rb.
Classification is metal.   Its color is silvery. 
It is really scarce.  It could change shapes. 
It is really expensive.  And it is hard to find.
                                                                                                             
BARIUM
The Symbol is Ba.
Its color is silvery white.
The classifacation is metal.
It is a very heavy metal.
It is used for rat poison.