- Rare metallic element - A rare nonmetallic element found in certain minerals, as
tantalite, samarskite, and fergusonite, and isolated as a dark powder
which becomes steel-gray by burnishing. Symbol Ta. Atomic weight 182.0.
Formerly called also tantalium.
- Rare metallic element - A rare metallic element of the boron-aluminium group,
found in gadolinite and other rare minerals, and extracted as a dark
gray powder. Symbol Y. Atomic weight, 89.
- A supposed rare metallic element, with a characteristic
spectrum, found associated with yttrium and other rare metals. Its
individuality and properties have not yet been determined.
- A rare metallic element, of uncertain identification,
supposed to exist in certain minerals, as gadolinite and samarskite,
with other rare ytterbium earth. Symbol Tr or Tb. Atomic weight 150.