What is the X in X-mas?
The symbol for the element ytterbium.
The symbol for ytterbium.
A soft, silvery-white metallic element of the lanthanide series that occurs as seven stable isotopes. It is used as a radiation source for portable x-ray machines. Atomic number 70; atomic weight 173.04; melting point 824°C; boiling point 1,196°C; specific gravity 6.972 or 6.54 (25°C) depending on allotropic form; valence 2, 3. See Periodic Table.
(Yb), chemical element, rare-earth metal of the lanthanoid series of the periodic table, a low-melting-point, divalent rare earth with little commercial use.