Terbium is a chemical element with symbol Tb and atomic number 65. It is a silvery-white, rare earth mGadolinium is a chemical element with symbol Gd and atomic number 64. Gadolinium is a silvery-white, malleable, and ductile rare earth metal.etal.

Atomic Weight: 3432
Density:       456 g/cm3
Melting Point: 54
Boiling Point: 453456