A rare element of the boron group, sometimes associated with yttrium or other related elements, as in euxenite and gadolinite. Symbol Yb; provisional atomic weight 173.2. Cf. Yttrium.
- A soft, bright, silvery rare-earth element occurring in two allotropic forms and used as an x-ray source for portable irradiation devices, in some laser materials, and in some special alloys. 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 Table at element.